## Summary

Follow up to #15563
Closes #13485

This is a first-pass at adding support for conditional support for Git
LFS between git sources, initial feedback welcome.

e.g.
```
[tool.uv.sources]
test-lfs-repo = { git = "https://github.com/zanieb/test-lfs-repo.git", lfs = true }
```

For context previously a user had to set `UV_GIT_LFS` to have uv fetch
lfs objects on git sources. This env var was all or nothing, meaning you
must always have it set to get consistent behavior and it applied to all
git sources. If you fetched lfs objects at a revision and then turned
off lfs (or vice versa), the git db, corresponding checkout lfs
artifacts would not be updated properly. Similarly, when git source
distributions were built, there would be no distinction between sources
with lfs and without lfs. Hence, it could corrupt the git, sdist, and
archive caches.

In order to support some sources being LFS enabled and other not, this
PR adds a stateful layer roughly similar to how `subdirectory` works but
for `lfs` since the git database, the checkouts and the corresponding
caching layers needed to be LFS aware (requested vs installed). The
caches also had to isolated and treated entirely separate when handling
LFS sources.

Summary
* Adds `lfs = true` or `lfs = false` to git sources in pyproject.toml
* Added `lfs=true` query param / fragments to most relevant url structs
(not parsed as user input)
  * In the case of uv add / uv tool, `--lfs` is supported instead
* `UV_GIT_LFS` environment variable support is still functional for
non-project entrypoints (e.g. uv pip)
* `direct-url.json` now has an custom `git_lfs` entry under VcsInfo
(note, this is not in the spec currently -- see caveats).
* git database and checkouts have an different cache key as the sources
should be treated effectively different for the same rev.
* sdists cache also differ in the cache key of a built distribution if
it was built using LFS enabled revisions to distinguish between non-LFS
same revisions. This ensures the strong assumption for archive-v0 that
an unpacked revision "doesn't change sources" stays valid.

Caveats
* `pylock.toml` import support has not been added via git_lfs=true,
going through the spec it wasn't clear to me it's something we'd support
outside of the env var (for now).
* direct-url struct was modified by adding a non-standard `git_lfs`
field under VcsInfo which may be undersirable although the PEP 610 does
say `Additional fields that would be necessary to support such VCS
SHOULD be prefixed with the VCS command name` which could be interpret
this change as ok.
* There will be a slight lockfile and cache churn for users that use
`UV_GIT_LFS` as all git lockfile entries will get a `lfs=true` fragment.
The cache version does not need an update, but LFS sources will get
their own namespace under git-v0 and sdist-v9/git hence a cache-miss
will occur once but this can be sufficient to label this as breaking for
workflows always setting `UV_GIT_LFS`.

## Test Plan

Some initial tests were added. More tests likely to follow as we reach
consensus on a final approach.

For IT test, we may want to move to use a repo under astral namespace in
order to test lfs functionality.

Manual testing was done for common pathological cases like killing LFS
fetch mid-way, uninstalling LFS after installing an sdist with it and
reinstalling, fetching LFS artifacts in different commits, etc.

PSA: Please ignore the docker build failures as its related to depot
OIDC issues.

---------

Co-authored-by: Zanie Blue <[email protected]>
Co-authored-by: konstin <[email protected]>