MNT: several updates to pyproject.toml, ignore uv.lock

[mwtoews]

Apologies for cobbling a few fixes into one PR.

These changes are related to PEP 639, and clear up deprecation warnings when building:

• Change [project.license] from a table to a SPDX license expression
• Add [project.license-files]
• Remove the license from the classifiers
• Correction [options.package_data] -> [tool.setuptools.package-data]

Other changes:

• Remove [tool.black], because target_version was incorrect (should be target-version), but more importantly this was tracking an old version of Python, and by default, Black will infer target versions from the project metadata (docs)
• Ignore uv.lock files, which are created with (e.g.) uv sync --all-extras