uv init normalize directory name

[j178]

Summary

Resolves #5255

[charliermarsh]

Do we reject packages with invalid names, like uv init "foo bar"? What happens there?

[konstin]

We may need to revisit the normalization for dots (e.g. foo.bar) later, but always using underscores doesn't seems correcter than the current solution

[j178]

Do we reject packages with invalid names, like uv init "foo bar"? What happens there?

error: Not a valid package or extra name: "foo bar". Names must start and end with a letter or digit and may only contain -, _, ., and alphanumeric characters.

It gets rejected during parsing to PackageName.