PR Review: #1372 — Replace tl.libdevice.llrint with tl.extra.cuda.libdevice.rint

[bug-fix] Triton API migration: updates tl.libdevice.llrint calls in 3 Triton quantization kernels to use the new tl.extra.cuda.libdevice path. The tl.libdevice namespace was removed in Triton 3.x, so this addresses a real compatibility issue.

Blocking issues (2):

1. Wrong function: rint instead of llrint — The PR replaces tl.libdevice.llrint with tl.extra.cuda.libdevice.rint, but these are semantically different functions. llrint rounds to the nearest integer and returns an integer type (long long). rint rounds to the nearest integer but returns a float. Since the result is being stored to an int8 output tensor, the practical difference may be minor (implicit float-to-int cast), but tl.extra.cuda.libdevice.llrint exists and is the correct 1:1 replacement. Using rint is an unnecessary semantic change that could introduce subtle numerical differences in edge cases (e.g., values exactly at 0.5 boundaries, NaN/Inf handling).

2. No regression test — This is a bug fix that changes quantization kernel behavior. There should be a test that exercises the Triton quantization path and verifies correctness. The bitsandbytes/triton/ kernels are guarded behind is_triton_available(), so existing tests may not exercise them. A minimal test confirming quantize_rowwise, quantize_global, and quantize_columnwise_and_transpose produce correct output with the updated API would be valuable.

Additional note: This PR is from September 2024 and is significantly behind main. A rebase will likely be needed. The Triton directory has had substantial changes since then (XPU triton optimizers, compatibility guards, etc.).

• Security: Clear (trivial API path change, no new imports, no suspicious patterns)
• Downstream impact: None (internal Triton kernels, not part of public API)
• Tests: Missing — no test covers the Triton quantization path change
• CI: Not triggered (fork PR — maintainer must approve workflow run)
• Serialization: Not affected
• Cross-PR conflicts: None detected