Add generate_identity_sequences helper and replace lambdas with named functors (#4828)

## Summary

- Add `generate_identity_sequences<N>()` helper that returns
`Tuple<Sequence<0>, Sequence<1>, ..., Sequence<N-1>>`
- Replace lambdas with named functors in `transform_tensor_descriptor`
- Add `unpack_and_merge_sequences` helper functor
- Reduces `transform_tensor_descriptor` instantiations from 388 to 32
(92% reduction)

## Motivation

Multiple call sites use `generate_tuple([](auto i) { return
Sequence<i>{}; }, Number<N>{})` pattern. A named helper reduces lambda
instantiations.

Additionally, each lambda in `transform_tensor_descriptor` creates a
unique closure type, causing the function to be instantiated separately
for every call site. Named functors share a single type, so the compiler
reuses the same instantiation.

## Changes

### Part 1: generate_identity_sequences helper
- Replaces common lambda pattern for generating identity sequences
- Each lambda expression creates a unique closure type, causing separate
template instantiations at every call site
- Named helper shares a single type across all uses

### Part 2: Named functors in transform_tensor_descriptor
- Add `unpack_and_merge_sequences` helper to replace lambda in
`GetNumOfHiddenDimension`
- Use `generate_identity_sequences` in `matrix_padder.hpp`

## Test Plan

- [x] Added 7 unit tests:
  - 4 tests for `generate_identity_sequences`
  - 3 tests for `unpack_and_merge_sequences`
- [ ] Waiting for full CI

## Related PRs

This PR merges the functionality from:
- ROCm/composable_kernel#3588 (generate_identity_sequences helper)
- ROCm/composable_kernel#3589 (Named functors in
transform_tensor_descriptor)

Part of PR stack for issue #4229 (Reduce CK/CKTile Build Times)

**Note:** This PR supersedes #4283, ROCm/composable_kernel#3588 and
ROCm/composable_kernel#3589, which can be closed once this is merged.

---
🔁 Imported from
[ROCm/composable_kernel#3628](https://github.com/ROCm/composable_kernel/pull/3628)
🧑‍💻 Originally authored by @tenpercent

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

include/ck/tensor_operation/gpu/thread/threadwise_tensor_slice_transfer_v3r1.hpp

@@ -739,8 +739,7 @@ struct ThreadwiseTensorSliceTransfer_v3r1
             },
             Number<nDim>{});
 
-        constexpr auto up_dim_idss =
-            generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<nDim>{});
+        constexpr auto up_dim_idss = generate_identity_sequences<nDim>();
 
         return transform_tensor_descriptor(desc0, transforms, low_dim_idss, up_dim_idss);
     }

include/ck/tensor_operation/gpu/thread/threadwise_tensor_slice_transfer_v3r1_dequant.hpp

@@ -894,8 +894,7 @@ struct ThreadwiseTensorSliceTransfer_v3r1_dequant
             },
             Number<nDim>{});
 
-        constexpr auto up_dim_idss =
-            generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<nDim>{});
+        constexpr auto up_dim_idss = generate_identity_sequences<nDim>();
 
         return transform_tensor_descriptor(desc0, transforms, low_dim_idss, up_dim_idss);
     }
@@ -944,8 +943,7 @@ struct ThreadwiseTensorSliceTransfer_v3r1_dequant
             },
             Number<nDim>{});
 
-        constexpr auto up_dim_idss =
-            generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<nDim>{});
+        constexpr auto up_dim_idss = generate_identity_sequences<nDim>();
 
         return transform_tensor_descriptor(desc0, transforms, low_dim_idss, up_dim_idss);
     }
@@ -993,8 +991,7 @@ struct ThreadwiseTensorSliceTransfer_v3r1_dequant
             },
             Number<nDim>{});
 
-        constexpr auto up_dim_idss =
-            generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<nDim>{});
+        constexpr auto up_dim_idss = generate_identity_sequences<nDim>();
 
         return transform_tensor_descriptor(desc0, transforms, low_dim_idss, up_dim_idss);
     }

include/ck/tensor_operation/gpu/thread/threadwise_tensor_slice_transfer_v3r1_gather.hpp

@@ -833,8 +833,7 @@ struct ThreadwiseTensorSliceTransfer_v3r1_gather
             },
             Number<nDim>{});
 
-        constexpr auto up_dim_idss =
-            generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<nDim>{});
+        constexpr auto up_dim_idss = generate_identity_sequences<nDim>();
 
         return transform_tensor_descriptor(desc0, transforms, low_dim_idss, up_dim_idss);
     }
@@ -892,8 +891,7 @@ struct ThreadwiseTensorSliceTransfer_v3r1_gather
             },
             Number<nDim>{});
 
-        constexpr auto up_dim_idss =
-            generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<nDim>{});
+        constexpr auto up_dim_idss = generate_identity_sequences<nDim>();
 
         return transform_tensor_descriptor(desc0, transforms, low_dim_idss, up_dim_idss);
     }

include/ck/tensor_operation/gpu/thread/threadwise_tensor_slice_transfer_v3r2.hpp

@@ -692,8 +692,7 @@ struct ThreadwiseTensorSliceTransfer_v3r2
             },
             Number<nDim>{});
 
-        constexpr auto up_dim_idss =
-            generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<nDim>{});
+        constexpr auto up_dim_idss = generate_identity_sequences<nDim>();
 
         return transform_tensor_descriptor(desc0, transforms, low_dim_idss, up_dim_idss);
     }
@@ -744,8 +743,7 @@ struct ThreadwiseTensorSliceTransfer_v3r2
             },
             Number<nDim>{});
 
-        constexpr auto up_dim_idss =
-            generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<nDim>{});
+        constexpr auto up_dim_idss = generate_identity_sequences<nDim>();
 
         return transform_tensor_descriptor(desc0, transforms, low_dim_idss, up_dim_idss);
     }

include/ck/tensor_operation/gpu/thread/threadwise_tensor_slice_transfer_v7r2.hpp

@@ -514,8 +514,7 @@ struct ThreadwiseTensorSliceTransfer_v7r2
             },
             Number<nDim>{});
 
-        constexpr auto up_dim_idss =
-            generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<nDim>{});
+        constexpr auto up_dim_idss = generate_identity_sequences<nDim>();
 
         return transform_tensor_descriptor(desc0, transforms, low_dim_idss, up_dim_idss);
     }
@@ -563,8 +562,7 @@ struct ThreadwiseTensorSliceTransfer_v7r2
             },
             Number<nDim>{});
 
-        constexpr auto up_dim_idss =
-            generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<nDim>{});
+        constexpr auto up_dim_idss = generate_identity_sequences<nDim>();
 
         return transform_tensor_descriptor(desc0, transforms, low_dim_idss, up_dim_idss);
     }

include/ck/tensor_operation/gpu/thread/threadwise_tensor_slice_transfer_v7r3.hpp

@@ -657,8 +657,7 @@ struct ThreadwiseTensorSliceTransfer_v7r3
             },
             Number<nDim>{});
 
-        constexpr auto up_dim_idss =
-            generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<nDim>{});
+        constexpr auto up_dim_idss = generate_identity_sequences<nDim>();
 
         return transform_tensor_descriptor(desc0, transforms, low_dim_idss, up_dim_idss);
     }
@@ -707,8 +706,7 @@ struct ThreadwiseTensorSliceTransfer_v7r3
             },
             Number<nDim>{});
 
-        constexpr auto up_dim_idss =
-            generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<nDim>{});
+        constexpr auto up_dim_idss = generate_identity_sequences<nDim>();
 
         return transform_tensor_descriptor(desc0, transforms, low_dim_idss, up_dim_idss);
     }

include/ck/tensor_operation/gpu/thread/threadwise_tensor_slice_transfer_v7r3_scatter.hpp

@@ -548,8 +548,7 @@ struct ThreadwiseTensorSliceTransfer_v7r3_scatter
             },
             Number<nDim>{});
 
-        constexpr auto up_dim_idss =
-            generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<nDim>{});
+        constexpr auto up_dim_idss = generate_identity_sequences<nDim>();
 
         return transform_tensor_descriptor(desc0, transforms, low_dim_idss, up_dim_idss);
     }
@@ -598,8 +597,7 @@ struct ThreadwiseTensorSliceTransfer_v7r3_scatter
             },
             Number<nDim>{});
 
-        constexpr auto up_dim_idss =
-            generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<nDim>{});
+        constexpr auto up_dim_idss = generate_identity_sequences<nDim>();
 
         return transform_tensor_descriptor(desc0, transforms, low_dim_idss, up_dim_idss);
     }