Optimize KDA prefill kernel (SM10X)

[icavan]

Description

Implement an optimized KDA prefill kernel for SM10X (Blackwell) GPUs.

Context

A fused KDA prefill kernel is already available for SM90 (Hopper). Porting and optimizing this for SM10X (Blackwell) would leverage Blackwell's architectural improvements for better inference performance.

Tasks

• Port the SM90 fused KDA prefill kernel to SM10X
• Optimize for Blackwell-specific features (TMEM. etc)
• Add correctness tests
• Benchmark