oxidize UV

[Byron]

Based on the content of the uv-git crate, which doesn't use git2 at all, but instead shells out to git.

Features

• init repo (without being tripped up by templates)
• deal with refspecs and references
• open any repository
• rev-parse
• fetch with credential handling, HTTPS/SSH (maybe local?) as in git fetch --tags --force --update-head-ok
  • However, it's not as compatible as Git, see [Azure Devops Repos] clone failure as packs use REF_DELTA objects: fix with git-style delta resolution #1025
  • checkout a tree
• clone into an empty directory, with checkout
• reset --hard
  • with submodule handling as in submodule update --recursive --init

Wanted features

Those are not a requirement to get started with the migration to gitoxide though.

• --filter=tree=0 support to not fetch blobs/fetch them later on demand (see this PR)
  • The above implies 'prefetch' support, so all needed objects can be fetched in bulk, on the fly.