Backtrack to non-local versions when wheels are missing platform support

[charliermarsh]

Summary

This is yet another variation on #9928, with a few minor changes:

1. It only applies to local versions (e.g., 2.5.1+cpu).
2. It only considers the non-local version as an alternative (e.g., 2.5.1).
3. It only considers the non-local alternative if it does support the unsupported platform.
4. Instead of failing, it falls back to using the local version.

So, this is far less strict, and is effectively designed to solve PyTorch but nothing else. It's also not user-configurable, except by way of using environments to exclude platforms.

[codspeed-hq]

CodSpeed Performance Report

Merging #10046 will not alter performance

_{Comparing charlie/incomplete-locals-only (6b79efd) with main (f3c5b63)}

Summary

✅ 14 untouched benchmarks

[BurntSushi]

Given PyTorch's setup, I feel comfortable with this. But if it's workable, I like @konstin's idea to use the complement of the implied markers instead of hard-coding the Windows/macOS/Linux platforms.