Allowlist the triton-kernels pure-Python sdist, and record why Windows on ARM is red

The two ubuntu2404 root legs went red at "Assert no source build" reporting
triton-kernels. That is not a regression in what the installer does. Those
builds have always happened; they only became visible now that pip_install
stopped discarding uv's output on success, which is what finally let the
nobuild check read the dependency phase at all.

So the question was whether each build actually needs a compiler. Checked
against the real artifacts rather than assumed:

  openai-whisper 20250625, randomname 0.2.1, argbind 0.3.9 -- no version of
  any of the three has ever published a wheel; antlr4-python3-runtime is
  pinned at 4.9.3, below the first release that ships one. All four sdists
  use setuptools.build_meta, declare no ext_modules, and contain no
  .c/.cpp/.pyx/.rs file. Already allowlisted, correctly.

  triton-kernels is the same category and was the only name failing. It is
  pinned to the triton repo's python/triton_kernels subdirectory; that tree
  is 75 files of Python, a four-line pyproject.toml, no setup.py and no
  native source at all. The kernels are Triton DSL compiled at runtime, not
  at install time. It is also a direct URL the installer names itself rather
  than something resolution picked, and only Linux reaches it. It belongs in
  the allowlist, so add it with that reasoning written down.

The allowlist match is now lowercased and underscore-folded on both sides.
The requirement spells the package triton_kernels while uv prints
triton-kernels, and an allowlist that matched only one spelling would pass
by luck rather than by intent. A plain pyarrow sdist is still caught.

The two data-designer @ file:// plugin builds needed nothing: they are
in-tree local paths, already dropped by the same rule that exempts the
source overlay's own build.

Separately, the windows-11-arm leg fails for a real reason and should keep
failing. The ARM handling itself works, the log shows torchaudio being
skipped and torch plus torchvision installing from wheels. What stops it is
that pyarrow and hf-transfer publish no win_arm64 wheel at all, so uv falls
back to their sdists and they fail on CMake configure and on openssl-sys
wanting perl. That is a product gap on the platform, not a gap in the
simulation, so the leg stays experimental and keeps reporting it. Record
that above the matrix entry so the next reader does not re-diagnose it.

.github/workflows/clean-machine-install-ci.yml

@@ -678,6 +678,17 @@ jobs:
             winget: 'masked'
             experimental: false
             overlay: true
+          # Windows on ARM gets as far as the dependency install and then stops on
+          # two packages that publish no win_arm64 wheel at all:
+          #   pyarrow==25.0.0  (pulled in by datasets) -- PyPI has win_amd64 only,
+          #     so uv falls back to the sdist and its CMake configure fails
+          #   hf-transfer==0.1.9 -- a maturin/Rust sdist whose openssl-sys build
+          #     script wants perl, which the image does not have
+          # The ARM-specific handling added for this platform is working: the log
+          # shows "windows on arm: skipping torchaudio", and torch 2.10.0+cpu and
+          # torchvision both install from wheels. The redness that remains is a
+          # real product gap on this platform, not a gap in the simulation, so the
+          # leg stays experimental and keeps reporting it rather than hiding it.
           - os: windows-11-arm
             winget: 'visible'
             experimental: true