Drop Python 3.7, update Black and Ruff, bump importlib-metadata

[ashleysommer]

Changed

• Dropped support for Python 3.7
  • Note, for compatibility with RDFLib 7.0, we specify a minimum Python version of v3.8.1
  • https://github.com/RDFLib/rdflib/blob/3bee979cd0e5b6efc57296b4fc43dd8ede8cf375/CHANGELOG.md?plain=1#L53
• Add preliminary support for Python 3.12
• Dropped support for RDFLib v6.2.0 and earlier
  • Only RDFLib v6.3.2 and v7.0 are supported by PySHACL v0.25.0+
• Bumped to updated version of Black and Ruff
  • Reformatted everything according to py38 codestyle

    Fixed

• Do not hard-pin to importlib-metadata. Fixes #214