Add type hints

[jodal]

I don't really expect a full review of this, but feel free to look around and
maybe check the branch out and try browsing the code in an IDE with good type
support, like VS Code with the Pylance extension with "Inlay Hints" enabled.

• Require Mopidy 4.0
• Make ruff enforce the presence of type hints
• Add type hints to everything
• Set up pyright in basic checking mode
• Fix pyright's basic warnings
• Move MpdContext out of dispatcher module
• Move util functions out of MpdDispatcher class
• Expose MpdUriMapper directly to protocol implementation
• Move subsystem events/subscriptions to MpdDispatcher
• Make MpdDispatcher use MpdSession directly
• Replace regexp pattern with full string matching
• Replace protocol_kwargs with something more type safe
• Properly type config object with MPD config
• Refactor command handler registration
• Work around too flexible typing of collections in models
• Work around lost type information
• Increase pyright's type checking mode to standard

[kingosticks]

I had a good go at a review. It all works fine as far as I can tell.

[jodal]

@kingosticks I've responded to or addressed all your comments now. Want to have another look?

[kingosticks]

LGTM