Bump pubgrub.

[Kaholaz]

This bump changes removes major parts of this packages public API. This is because this functionality is duplicated in the gleam repo and I thus see no reason to maintain it two places. Let me know if you disagree. Here are the parts of the API that were slashed:

version::pubgrub_report;
version::Version::bump;
version::PackageVersions;
version::resolve_versions;
version::PackageFetcher;

I also changed version::Range to be parsed at creation instead of at use. This removes some unnecessary error handling in resolution of dependency. This seems more sensible.