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/wrapper/utils/layout_utils.hpp

@@ -186,8 +186,7 @@ __host__ __device__ constexpr auto get(const Layout<Shape, UnrolledDesc>& layout
         },
         Number<old_shape_dims>{});
 
-    const auto lower_dims =
-        generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<old_shape_dims>{});
+    const auto lower_dims = generate_identity_sequences<old_shape_dims>();
     const auto upper_dims = generate_tuple(
         [&](auto i) {
             if constexpr(i < shape_offset || i >= shape_offset + new_shape_dims)
@@ -492,8 +491,7 @@ __host__ __device__ constexpr auto unmerge(const Layout<Shape, UnrolledDesc>& la
         },
         Number<dims>{});
 
-    constexpr auto lower_dims =
-        generate_tuple([&](auto i) { return Sequence<i.value>{}; }, Number<dims>{});
+    constexpr auto lower_dims = generate_identity_sequences<dims>();
     constexpr auto upper_dims = generate_tuple(
         [&](auto i) {
             if constexpr(is_detected<is_tuple, tuple_element_t<i.value, NewIdxs>>::value)

include/ck/wrapper/utils/tensor_partition.hpp

@@ -293,8 +293,7 @@ make_local_partition(TensorType& tensor,
         },
         Number<remove_reference_t<decltype(tensor_shape)>::Size()>{});
     const auto lower_upper_dims =
-        generate_tuple([&](auto i) { return Sequence<i.value>{}; },
-                       Number<remove_reference_t<decltype(tensor_shape)>::Size()>{});
+        generate_identity_sequences<remove_reference_t<decltype(tensor_shape)>::Size()>();
     auto sliced_desc =
         transform_tensor_descriptor(unrolled_desc, transforms, lower_upper_dims, lower_upper_dims);
     // Create layout