Recognize build tags in wheel data directories

[lin-hongkuan]

Fixes #193.

This updates WheelFile.data_dir to include the optional wheel build tag parsed from the wheel filename, so files under directories such as foo-0.4.2-1337.data/ are routed through the wheel .data scheme instead of being treated as root-scheme files.

The base WheelSource behavior is unchanged for callers that construct sources without a wheel filename.

Tests added:

• WheelFile.data_dir includes the build tag for build-tagged wheels.
• install() routes a build-tagged wheel data file to the data scheme.

Checks run locally:

• PYTHONPATH=src python -m pytest tests\test_sources.py::TestWheelFile::test_build_tag_is_part_of_data_dir tests\test_core.py::TestInstall::test_handles_wheel_data_dir_with_build_tag -q
• PYTHONPATH=src python -m pytest tests\test_sources.py tests\test_core.py -q
• PYTHONPATH=src python -m pytest -q
• python -m ruff check src tests
• python -m ruff format --check src tests
• PYTHONPATH=src python -m mypy src
• git diff --check

[yangfan-yf-yf]

The optional build tag belongs only in the wheel filename. The wheel specification defines the data directory as the dist-info directory name with the extension changed to .data, so a build-tagged wheel still uses distribution-version.data.

Changing WheelFile.data_dir to include self._build_tag makes a compliant wheel such as fancy-1.0.0-1337-py3-none-any.whl with fancy-1.0.0.data/data/... no longer match the data scheme. The new fixture and assertions instead encode the non-standard fancy-1.0.0-1337.data layout.

Could this preserve the required distribution-version.data handling for build-tagged wheels? If compatibility with legacy non-standard artifacts is desired, it needs to be additive rather than replacing the standard directory name, with regression coverage for both layouts.