Support reading Python versions from tool.uv

[zanieb]

#4335 adds support for Python version files, but we should also support a section in the pyproject.toml with more structured data.

[TommasoAmici]

for projects with multiple languages/tools, it's possible to have the python version in a .tool-versions file which is very similar in spirit to .python-versions, I don't think uv currently supports this and I can't find an existing issue. I suppose this is more of a feature request, though.

e.g.:
https://asdf-vm.com/manage/configuration.html#tool-versions
https://mise.jdx.dev/configuration.html#tool-versions

[zanieb]

@TommasoAmici would you mind opening a dedicated issue for supporting that?

[TommasoAmici]

sure! #6574