### Context
See https://github.com/beetbox/beets/pull/5916 where we've come across a
need to define common logic between `TrackInfo` and `AlbumInfo`.
### Changes
- Introduce generic `Info` base (extends `AttrDict`) used by `AlbumInfo`
/ `TrackInfo` to centralize shared attributes and initialisation logic.
- Sort keyword parameters in each constructor alphabetically and make
them explicit.
- Deduplicate and simplify shared `copy()` method using `copy.deepcopy`
- Improve type hints and documentation.
- Drop unused logging artifacts.
## Summary by Sourcery
Refactor metadata-handling classes by extracting common functionality
into a new Info base, updating AlbumInfo and TrackInfo to extend it with
explicit sorted parameters, unify their copy logic, improve type
annotations and docs, and drop obsolete logging code
New Features:
- Introduce a generic Info base class to centralize shared logic for
AlbumInfo and TrackInfo
Enhancements:
- Alphabetically sort and explicitly declare constructor keyword
parameters for consistency
- Unify and simplify the copy() implementation in AttrDict using
deepcopy
- Enhance type hints and documentation for metadata classes
Chores:
- Remove unused logging imports and artifacts
This PR includes documentation updates for the new `metadatasource`
plugin architecture, as requested by @snejus. The docs changes were
split out from the original implementation to keep things focused and
reviewable.
* Introduces comprehensive documentation for the new metadata plugin
system.
* Performs a general cleanup of the plugin-related developer
documentation for clarity and consistency.
* Splits and cleanup for quite some files in the dev docs
- Add configurable `search_limit` option to Deezer and Spotify plugins
(default 5) and enforce it when returning search results.
- Rename `musicbrainz.searchlimit` to `musicbrainz.search_limit` (old
key still read with deprecation warning; slated for removal in 3.0.0).
- Update docs and changelog to reflect the changes.
This PR modernizes the codebase by replacing all `str.format()` calls,
`%` operator, and most of string concatenation with f-string literals.
Fixes#5293
Supersedes #5337
Once this is reviewed, I will squash all commits into one and add the
hash to `.git-blame-ignore-revs` file.
