Bump pubgrub.

[Kaholaz]

This PR requires gleam-lang/hexpm-rust#43. Create a symlink named hexpm in the root of the project linking to my hexpm-rust branch to look at my changes. Cargo.toml needs to be cleaned before a merge.

Most changes are one of these three types of changes:

1. Accommodating the hexpm-rust change that parses hexpm::version::Range.
2. Changing imports to coincide with the 0.3 structure of pubgurb.
3. Changes to the dependency resolution due to changes to the pubgrub::DependencyProvider trait.

Out of those, I believe nr. 3 warrants the most explanation (2. is explained in the hexpm-rust pull request -- let me know if anything is unclear). The major changes include choose_package_version of pubgrub::DependencyProvider being split into the functions choose_version and prioritize, and the trait requiring the the associated type Err: Error + 'static. The changes to the choose_package_version, might be the hardest one to get correct, but all tests are passing so I think we are good. The change to the associated Err type required a new error type and caused this to propagate a bit. I don't know if this is the best way to do it, but it does the job :D

Again: Let me know if anything is unclear or if you want me to write a more detailed changelog.

[lpil]

I have published the new package as v4!

[Kaholaz]

I have published the new package as v4!

@lpil nice :D I rebased and tested the changes.

[lpil]

Wonderful!! Thank you! I've left a couple notes inline

[lpil]

Hello! Thank you for this. I just published that new hexpm package, is there a small upgrade to do in this PR now that can be used?

[Kaholaz]

@lpil Thank you; I have used the hexpm update to avoid a call to clone :D

[lpil]

Some linter issues to resolve!

[lpil]

Bravo!! Thank you very much!