oxidize `built`

[Byron]

API

• describe HEAD
  • with dirty suffix (no untracked, based on otherwise complete status (tree-index, index-worktree))
• branch name of current head

For tests

Author seems open to switch to gix-testtools, even though it seems fine to just keep the git2 version unless the removal of git2 as feature is desired at some point.

• init repository
• add worktree file to index
• create a commit from changed index
• create tag
• detach head with worktree update

Implementation

• initial work: Add gitoxide feature lukaslueg/built#52
• integration check: Add gitoxide backend Byron/built#1 (let's not bother the author while dirty isn't present)