metadata_directory already contains dist-info directory

[konstin]

From PEP 517:

def prepare_metadata_for_build_wheel(metadata_directory, config_settings=None):
    ...

Must create a .dist-info directory containing wheel metadata inside the specified metadata_directory (i.e., creates a directory like {metadata_directory}/{package}-{version}.dist-info/).

def build_wheel(wheel_directory, config_settings=None, metadata_directory=None):
    ...

If the build frontend has previously called prepare_metadata_for_build_wheel and depends on the wheel resulting from this call to have metadata matching this earlier call, then it should provide the path to the created .dist-info directory as the metadata_directory argument.

Notice that the metadata_directory is different for the both hooks: For prepare_metadata_for_build_wheel is doesn't contain the .dist-info directory as final segment, for build_wheel it does.

Previously, the code assumed that both directories didn't contain the .dist-info for both cases.

Checked with:

maturin build
uv init test-uv-build-backend --build-backend uv
cd test-uv-build-backend
uv build --sdist --preview
cd ..
UV_PREVIEW=1 pip install test-uv-build-backend/dist/test_uv_build_backend-0.1.0.tar.gz --no-index --find-links target/wheels/ -v --no-cache-dir

Fixes #9969