[Feature Request] MLADecodeWithKVCacheOp implementation

[xZacky]

Parent Issue

Part of #111

Task Type

• L2: Op Implementation (Wrapper + Unit Tests + Benchmarks)

Description

Checklist

• Implementation follows Google Python Style for code and docstrings.
• (L2 Only) Unit tests match PyTorch reference (FP16/BF16).
• (L2 Only) Benchmarks implemented (Latency/TFLOPS/Bandwidth).