[CK][CK_TILE] Fix dispatcher cpp tests - registry key mismatch and string assertions (#6528)

## Motivation

CPP tests in dispatcher were failing due to a mismatch in registry key
and string representation.

## Technical Details
Bug 1 - Registry key mismatch: The registry stored kernels using
get_name() but lookups used encode_identifier(), causing all registry
lookups to fail. Fixed by changing registry.cpp:58 to use
encode_identifier() for storage.
Bug 2 - String representation changes: Tests checked for
"persist"/"nopers" substrings, but the code emits "True"/"False". Fixed
by replacing brittle substring checks with comparison-based assertions
in test_kernel_key.cpp and test_kernel_key_extended.cpp.

## Test Plan

Tested with CPP tests in dispatcher 

## Test Result

Validation: All three core cpp tests now pass:
  - test_kernel_key - 6/6 tests passing
  - test_kernel_key_extended - 25/25 tests passing
  - test_registry - 8/8 tests passing
  
 
## Submission Checklist

- [ x] Look over the contributing guidelines at
https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.

---------

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

dispatcher/codegen/unified_grouped_conv_codegen.py

@@ -600,7 +600,7 @@ struct {kernel_name}_Launcher {{
             GroupedConvTraitsType::FixedGemmParams::TransposeC,
             Config::NumWaveGroups,
             GroupedConvTraitsType::FixedGemmParams::FixedVectorSize,
-            Config::VectorSizeC, false, 1, Config::DoubleSmemBuffer>>;
+            Config::VectorSizeC, 1, Config::DoubleSmemBuffer>>;
         
         using Kernel = {kernel_type}<
             GroupedConvTraitsType, TilePartitioner, GemmPipeline, ConvEpilogue>;