feat: uv --directory support for locking

[aignas]

With this PR we will be able to decouple how the locking rule is working from
which BUILD.bazel file contains the rule. This means that we can have duplicate
invocations in the examples/bzlmod and examples that would yield exactly
the same thing, allowing us to essentially migrate all of the invocations of
compile_pip_requirements everywhere to the lock rule.

The goal is to ensure that all of the following invocations can have the same
output:

• bazel run <lock_target>.run
• bazel run <lock_target>.update
• uv <cmd>

Summary:

• Add uv pip compile --directory support on UNIX.
• Add uv lock --directory support on UNIX.
• Add uv pip compile --directory support on Windows.
• Add uv lock --directory support on Windows.
• Add integration tests for various setups in tests/uv.
• Add unit tests for the code to ensure the paths are correctly remapped.

[aignas]

@rickeylev, if you wish, you could point your agent at this. It would be great to finish the Windows parts. This should make it possible to have the lock rule used for example lock regeneration and it should be invariant where we are running the lock. We could also build on top of this for the uv workspace files.