Implement service config abstraction

[semohr]

This pull request introduces a major refactor to the configuration system, making service configuration dynamic and extensible. Instead of having a static config schema with hardcoded service fields, the config schema is now built at runtime based on registered ServiceConfig subclasses. This enables easier addition of new services, more flexible config validation, and improved modularity. The changes also update service modules to register their config schemas and update all relevant usages.

TODO:

• Docs need changes (most notebooks and a general config page would be nice)

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[codecov]

Codecov Report

❌ Patch coverage is 81.56028% with 26 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
plistsync/services/plex/authenticate.py	0.00%	6 Missing ⚠️
plistsync/services/plex/config.py	82.35%	3 Missing ⚠️
plistsync/services/spotify/authenticate.py	0.00%	3 Missing ⚠️
plistsync/services/tidal/authenticate.py	0.00%	3 Missing ⚠️
plistsync/config.py	96.72%	1 Missing and 1 partial ⚠️
plistsync/services/plex/api.py	33.33%	2 Missing ⚠️
plistsync/services/spotify/api.py	0.00%	2 Missing ⚠️
plistsync/services/tidal/api.py	0.00%	2 Missing ⚠️
plistsync/services/spotify/config.py	90.00%	1 Missing ⚠️
plistsync/services/tidal/config.py	90.90%	1 Missing ⚠️
... and 1 more

📢 Thoughts on this report? Let us know!