Add Git LFS support to `uv-git` crate (#10335)
## Summary
Closes #3312.
This PR adds Git LFS support to the `uv-git` crate by using the
`git-lfs` CLI to fetch required LFS objects for a revision following the
call to `git fetch`.
The LFS fetch step is disabled by default and only enabled if the
environment variable `UV_GIT_LFS` is set.
When enabled, the LFS fetch step is run for all repositories regardless
of whether they have associated LFS objects. The step is skipped if the
`git-lfs` CLI tool isn't installed.
## Test Plan
I verified that the minimal example in the linked issue passes, i.e.
this command now succeeds:
```sh
UV_GIT_LFS=1 uv pip install git+https://github.com/grebnetiew/lfs-py.git
```
I also verified that non-LFS repositories still work, with or without
`git-lfs` installed.
### To Replicate
Attempt to use uv to install a Git dependency that contains LFS objects
(e.g. `uv pip install git+https://github.com/grebnetiew/lfs-py.git`).
This should fail with a smudge filter error.
Re-run the same command with the added environment variable
`UV_GIT_LFS=1`. The install should now succeed.
## Potential Changes / Improvements
~With this change LFS objects in a given revision will always be
downloaded if the user has Git LFS installed, which may not always be
desired behavior. It might be helpful to add a field to the `uv`
settings and/or an environment variable so that the LFS step can be
disabled if needed.~
Enabling/disabled via environment variable has now been implemented.
---------
Co-authored-by: Sydney Duckworth <sydduckworth@users.noreply.github.com>
Co-authored-by: Zanie Blue <contact@zanie.dev>
