Disable sam_fast custom flash without Triton block pointers

[warrendeng]

The optional segment-anything-fast flash_4 kernel still uses Triton's legacy tl.make_block_ptr and tl.advance APIs, which were removed by triton-lang/triton#10833. This causes the full sam_fast TorchBench model to fail during eager validation with newer Triton revisions.

Detect those APIs before importing segment_anything_fast and use its documented SEGMENT_ANYTHING_FAST_USE_FLASH_4=0 switch when they are unavailable. The benchmark continues exercising the full model through its existing SDPA fallback, while older Triton behavior remains unchanged.

Test plan:

• python3.12 -m py_compile torchbenchmark/models/sam_fast/__init__.py
• Verified with Triton 3.7 that the custom kernel remains enabled when both APIs exist
• Simulated missing tl.advance and verified the adapter disables the custom kernel before package import

[warrendeng]

Superseded by #2701, which uses a branch in pytorch/benchmark so the repository CI credentials are available.