Maintenance: modernize tooling, fix mpdscribble_history import bug

[dbeley]

Summary

This PR brings several maintenance updates to the project:

Bug Fix

• mpdscribble_history.py: Fixed import create_network → create_networks (the function was renamed in utils.py but the import in mpdscribble_history.py was not updated, causing an ImportError at runtime).

Project Modernization

• pyproject.toml: Migrated project metadata from setup.py to the modern [project] section (name, version, dependencies, classifiers, scripts, URLs). Added [tool.pytest.ini_options] for test discovery.
• setup.py: Reduced to a minimal single-line setup() call, deferring all metadata to pyproject.toml.
• Dependencies: Added minimum version bounds (httpx>=0.28.0, python-mpd2>=3.0.0, pylast>=5.0.0). Bumped requires-python to >=3.9.

CI & Tooling

• CI: Updated actions/checkout v2→v4, actions/setup-python v2→v5, codecov-action v1→v5. Removed EOL Python 3.7/3.8, added 3.12/3.13.
• Pre-commit: Updated pre-commit-hooks v4.5.0→v5.0.0, black 23.3.0→25.1.0, flake8 6.0.0→7.1.1.
• shell.nix: Replaced pipenv-based shell with modern venv-based approach.
• __init__.py: Removed unnecessary shebang, encoding declaration, and unused name variable.

Testing

All 8 existing tests pass with the updated configuration.