fix(uv): Don't just delete windows whls

[arrdem]

Summary

Packages with only platform-specific wheels (e.g. Windows-only) and no source distribution would crash with an empty select chain when built on an incompatible host.

• Adds _no_sbuild filegroup marked target_compatible_with = ["@platforms//:incompatible"] as the default arm when no sdist fallback exists
• Adds win32, win_amd64, and win_arm64 platform config_settings (with msvc libc) so Windows wheels are included in the select chain rather than silently dropped
• Adds is_msvc config_setting and makes is_musl visibility public

This doesn't enable full Windows builds (no interpreter support yet), but cross-platform lockfiles containing Windows-only packages no longer break analysis on Linux/macOS.

Fixes #754

Test plan

• bazel test //... — 87/87 pass
• e2e //cases/uv-no-sdist-754:test — verifies pywin32 repo has _no_sbuild incompatible default and Windows wheel arms

🤖 Generated with Claude Code

[aspect-workflows]

Bazel 8 (Test)

All tests were cache hits

87 tests (100.0%) were fully cached saving 47s.

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Bazel 9 (Test)

All tests were cache hits

87 tests (100.0%) were fully cached saving 1m 15s.

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Bazel 8 (Test)

e2e

All tests were cache hits

20 tests (100.0%) were fully cached saving 12s.

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Bazel 9 (Test)

e2e

All tests were cache hits

20 tests (100.0%) were fully cached saving 14s.

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Bazel 8 (Test)

examples/uv_pip_compile

All tests were cache hits

1 test (100.0%) was fully cached saving 444ms.

[arrdem]

Blocked on #776 probably.

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