[CK_BUILDER] validation (#3471)

This pull request builds on #3267 by proving the "validation" infrastructure, the means to compare a set of `Outputs`.

The design of the validation infrastructure is relatively straight forward:
- Each SIGNATURE should come with a `validate()` implementation, which should be implemented in a similar way that the other functions/types from `testing.hpp` are implemented.
- `validate()` returns a `ValidationReport`, which is a structure that keeps all relevant information about comparing the tensors from two `Outputs`. Note that crucially, `validate()` should not do any reporting by itself. Rather, glue logic should be implemented by the user to turn `ValidationReport` into a relevant error message.
- You can see this clue code for CK-Builder itself in `testing_utils.hpp`, its `MatchesReference()`. This functionality is relatively barebones right now, it will be expanded upon in a different PR to keep the scope of this one down.

The comparison is done on the GPU (using an atomic for now), to keep tests relatively quick. Some notable items from this PR:
- To help compare the tensors and with writing tests, I've written a generic function `tensor_foreach` which invokes a callback on every element of a tensor.
- For that it was useful that the `TensorDescriptor` has a rank which is known at compile-time, so I've changed the implementation of `TensorDescriptor` for that. I felt like it was a better approach than keeping it dynamic, for multiple reasons:
  - This is C++ and we should use static typing where possible and useful. This way, we don't have to implement runtime assertions about the tensor rank.
  - We know already know the rank of tensors statically, as it can be derived from the SIGNATURE.
  - It simpifies the implementation of `tensor_foreach` and other comparison code.
- There are a lot of new tests for validating the validation implementation, validating validation validation tests (Only 3 recursive levels though...). For a few of those functions, I felt like it would be useful to expose them to the user.
- Doc comments everywhere.

experimental/builder/test/CMakeLists.txt

@@ -80,33 +80,36 @@ add_ck_builder_test(test_ckb_conv_builder
     test_instance_traits_util.cpp
     unit_device_buffer.cpp
     unit_tensor_descriptor.cpp
+    unit_tensor_foreach.cpp
+    unit_error.cpp
+    unit_validation.cpp
     unit_conv_elementwise_op.cpp
     unit_conv_tensor_layout.cpp
     unit_conv_tensor_type.cpp
     unit_conv_thread_block.cpp
     unit_conv_tuning_params.cpp)
-    
-    # Tests the inline diff utility used for comparing strings in tests assertions
-    add_ck_builder_test(test_ckb_inline_diff test_inline_diff.cpp)
 
-    # GPU reference validation tests (in validation/ folder)
-    # 1. Reference kernel execution and InstanceTraits
-    add_ck_builder_test(test_ckb_reference_execution 
-        validation/test_reference_execution.cpp
-        validation/test_reference_instance_traits.cpp)
-    target_link_libraries(test_ckb_reference_execution PRIVATE utility)
-    
-    # Note: Optimized kernel validation tests will be added after merging dev branch
-    # with kernel Run() implementation from colleague's work
+# Tests the inline diff utility used for comparing strings in tests assertions
+add_ck_builder_test(test_ckb_inline_diff test_inline_diff.cpp)
+
+# GPU reference validation tests (in validation/ folder)
+# 1. Reference kernel execution and InstanceTraits
+add_ck_builder_test(test_ckb_reference_execution
+    validation/test_reference_execution.cpp
+    validation/test_reference_instance_traits.cpp)
+target_link_libraries(test_ckb_reference_execution PRIVATE utility)
+
+# Note: Optimized kernel validation tests will be added after merging dev branch
+# with kernel Run() implementation from colleague's work
+
+# Tests convolution trait selection and configuration
+add_ck_builder_test(test_ckb_conv_traits
+    conv/ck/test_conv_traits.cpp)
+
+# Tests convolution problem description and parameter handling
+add_ck_builder_test(test_ckb_conv_description
+    test_conv_description.cpp)
 
-    # Tests convolution trait selection and configuration
-    add_ck_builder_test(test_ckb_conv_traits
-        conv/ck/test_conv_traits.cpp)
-    
-    # Tests convolution problem description and parameter handling
-    add_ck_builder_test(test_ckb_conv_description
-        test_conv_description.cpp)
-    
 ################################################################################
 # REGRESSION TESTS - Integration Tests (With Kernel Compilation)
 ################################################################################