[REQ] pip: add support for per-package binary/source selection

[bchuo]

What kind of request is this?

None

What is your request or suggestion?

The pip generator cannot selectively apply --no-binary to a single package. The current approach uses an image source with cmd to:

• Download all wheels (including numpy wheel) via pip download
• Replace the numpy wheel with sdist fetched directly from PyPI JSON API
• Download build deps (meson, cython, etc.) for the subsequent compile stage

Reference: https://github.com/Azure/dalec-build-defs/pull/10132#discussion_r3401754699

Are you willing to submit PRs to contribute to this feature request?

• Yes, I am willing to implement it.

[cpuguy83]

The thing is we don't want binaries in the sources.
Allowing the spec author to do what they need to do is fine, but those sources get added to source packages which should be buildable on multiple platforms.