feat(backend): Add MaskPattern-based TSCATTER instruction and system tests

[Crystal-wzy]

Add a new TSCATTER overload that accepts a MaskPattern template parameter
(P0101, P1010, P0001, P0010, P0100, P1000, P1111), mirroring the existing
TGATHER MaskPattern interface. The implementation scatters source elements
into destination positions selected by the mask, zeroing non-selected slots.

Summary

• Add TSCATTER<maskPattern>(dst, src, events...) template in common,
  costmodel, and cpu backends
• Implement TScatter and TSCATTER_IMPL in TScatter.hpp with
  static assertions for 16/32-bit element width, Vec tile type, and
  row-major layout
• Add tscatter_common.h shared header for masked test infrastructure
• Add gen_data.py golden-data generator covering all 7 mask patterns
  for float32, float16, uint16, int16, uint32, and int32 types
• Add parametrized GTest cases in main.cpp and kernel implementations
  in tscatter_kernel.cpp
• Fix inconsistent WaitEvents &... events spacing to WaitEvents &...events
  across costmodel pto_instr.hpp

Testing

• All masked TSCATTER parametrized test cases pass
• Existing TSCATTER index-based test unaffected
• Pre-commit hooks pass

[gemini-code-assist]

Code Review

This pull request introduces the TSCATTER instruction across the common, cost model, and CPU implementations, along with comprehensive unit tests for masked scatter operations. The review feedback identifies a significant bug in the test logic where vector sizing and type handling for half-precision data are incorrect. Additionally, the reviewer pointed out potential memory access safety issues in the CPU implementation's indexing logic and a redundant pointer assignment in the test kernel.