Allow download of Python distribution variants with newer CPU instruction sets (#9781)
Supersedes https://github.com/astral-sh/uv/pull/8517 with an alternative
approach of making all the variants available instead of replacing the
x86_64 (v1) variant with x86_64_v2.
Doesn't add automatic inference of the supported instructions, but that
should be doable per @charliermarsh's comment there. Going to do it as a
follow-up since this has been pretty time consuming.
e.g.,
```
❯ cargo run -q -- python install cpython-3.12.8-linux-x86_64_v3-gnu
Installed Python 3.12.8 in 2.72s
+ cpython-3.12.8-linux-x86_64_v3-gnu
```
Co-authored-by: j178 <10510431+j178@users.noreply.github.com>