test: skip NVFP4-KV decode tests on SM107

[Vinnie6167]

What

Adds a skip_if_nvfp4_kv_unsupported() helper to tests/attention/test_batch_decode_kernels.py and calls it at the top of test_batch_decode_with_paged_kv_cache_nvfp4, skipping the NVFP4-KV decode tests on SM107 (compute capability (10, 7)).

Why

NVFP4 KV-cache decode is deliberately unsupported on SM107: #4122 (Adds SM107 support) added guards in flashinfer/decode.py and flashinfer/prefill.py that raise ValueError("KV Cache NVFP4 is not supported on SM107") for any packed-FP4 (uint8) KV cache on that arch. These tests exercise the FA2 tensor-cores decode path (use_tensor_cores=True) with NVFP4 KV, so on Rubin hardware all 289 nvfp4 ids in this file currently fail with that exact ValueError instead of skipping:

[289 failed, 2970 passed] ValueError: KV Cache NVFP4 is not supported on SM107 (x289)

(full release-v0.6.16 sweep on VR200, 2026-07-28)

Notes

• The skip keys on == (10, 7) to mirror the library guard exactly — it skips precisely where the library declares unsupported, nowhere else.
• All nvfp4 entry points route through test_batch_decode_with_paged_kv_cache_nvfp4 (including the _large_head variant and the torch-compile smoke test), so the single call site covers all 289 ids.
• Related but distinct: the trtllm-gen backend has its own NVFP4-KV gap on SM107 (published E2m1-KV FMHA kernels exist only for Sm100a/103a). That affects the trtllm-gen decode test files, not this one.
• When NVFP4-KV support lands for SM107, lifting this skip belongs to the same change that lifts the library guard.

🤖 Generated with Claude Code

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