[Performance]: FalshInfer attn backend. Use dynamic AttentionCGSupport

[vadiklyutiy]

Proposal to improve performance

Right now FlashInfer attn backend uses AttentionCGSupport.UNIFORM_SINGLE_TOKEN_DECODE that doesn't allow to use FULL cudagraph in case if speculative decoding.

In fact FlashInfer contains several attn those chose dynamically. TRT_LLM Gen backend (one of the fastest) supports speculative decoding (AttentionCGSupport.UNIFORM_BATCH) and it does make sense to enable cudagraph for decode phase.

[vadiklyutiy]

@benchislett