Use Metadata10 to parse PKG-INFO of legacy editable (#3450)
It turns out setuptools often uses Metadata-Version 2.1 in their
PKG-INFO:
https://github.com/hauntsaninja/setuptools/blob/4e766834d72623f3b938f1d4148547ea73af1bf5/setuptools/dist.py#L64
`Metadata23` requires Metadata-Version of at least 2.2.
This means that uv doesn't actually recognise legacy editable
installations from the most common way you'd actually get legacy
editable installations (works great for most legacy editables I make at
work though!)
Anyway, over here we only need the version and don't care about anything
else. Rather than make a `Metadata21`, I just add a version field to
`Metadata10`. The one slightly tricky thing is that only
Metadata-Version 1.2 and greater guarantee that the [version number is
PEP 440 compatible](https://peps.python.org/pep-0345/#version), so I
store the version in `Metadata10` as a `String` and only parse to
`Version` at time of use.
Also did you know that back in 2004, paramiko had a pokemon based
versioning system?
