The pip-specific Path implementation has been removed, and all its
usages replaced by pathlib.Path. The tmpdir and tmpdir_factory fixtures
are also removed, and all usages are replaced by tmp_path and
tmp_path_factory, which use pathlib.Path.
The pip() function now also accepts pathlib.Path so we don't need to put
str() everywhere. Path arguments are coerced with os.fspath() into str.
In the base class, the signature is defined as:
type: (str) -> str
Further, the docstring says:
Raises RemoteNotFoundError if the repository does not have a remote
url configured.
However, some subclasses were returning None instead of raising
RemoteNotFoundError. This violated the type signature and forced calling
code to handle multiple error paradigms.
Now, all subclasses implement the base's signature.
This allowed simplifying some call sites as they can assume None will
not be returned.
This mismatch was noticed while trying to remove "mypy:
disallow-untyped-defs=False" comments.
This significantly improves performance, since it allows the remote
server to directly stream a tarball that just contains the requested
revision rather than the full repository contents.
