Dedupe individual tracks during import based on stable identifier

[tommyschnabel]

Description

This PR adds the duplicate_track_resolution (bool) and duplicate_track_action (skip, remove, keep/merge, ask) config options to import to enable deduplication of individual tracks when importing.

The recommended config for this is:

import:
    duplicate_track_resolution: yes
    duplicate_action: ask          # whole-album duplicates
    duplicate_track_action: skip   # per-track duplicates: fold new tracks into the existing album
    duplicate_keys:
        item: mb_trackid           # match on a stable id (recommended when autotagging)

With the above config, any duplicate imports of tracks will be dropped, and if the whole album has been imported before, the album import itself will be dropped. If part of an album is deduped, the new tracks will be folded into the existing album. This config allows for idempotency on any repeat beet import executions.

Copied from the new docs, here's what each option does:

skip drops the duplicate tracks and adds the remaining new tracks to the
existing album they belong to, instead of importing them as a separate album.
Use this to complete a partially-imported album. If every track is already
present, the whole album is skipped. (If the matching tracks do not all belong
to a single album, the new tracks are imported as their own album.)

• remove removes the matching old items from the library before importing.
• keep (and merge) import the album unchanged.
• ask prompts you to choose one of the above.

The duplicate_keys config option is what's used to dedupe, so set it to something stable like mb_trackid.

In the previous PR, @snejus suggested adding this as an addition to the album deduplication that already exists. This implementation is separate from the album dedupe logic because the use-cases seemed incompatible.

The album dedupe skips/merges/removes based on an album already being imported, but the use-case I wanted was a deeper track-based mechanism. Bolting this onto the album dedupe produced some really weird results, and I wasn't able to achieve parity with my last impl with the available config options. This is a better, more flexible, approach.

To Do

• Documentation. (If you've added a new command-line flag, for example, find the appropriate page under docs/ to describe it.)
• Changelog. (Add an entry to docs/changelog.rst to the bottom of one of the lists near the top of the document.)
• Tests. (Very much encouraged but not strictly required.)

[codecov]

Codecov Report

❌ Patch coverage is 75.53191% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.63%. Comparing base (6f8d55d) to head (b79ac79).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
beets/ui/commands/import_/session.py	6.66%	14 Missing ⚠️
beets/importer/tasks.py	81.48%	2 Missing and 3 partials ⚠️
beets/importer/stages.py	92.00%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6723      +/-   ##
==========================================
- Coverage   75.63%   75.63%   -0.01%     
==========================================
  Files         162      162              
  Lines       20820    20903      +83     
  Branches     3298     3322      +24     
==========================================
+ Hits        15747    15809      +62     
- Misses       4292     4310      +18     
- Partials      781      784       +3     

Files with missing lines	Coverage Δ
beets/importer/session.py	94.40% <100.00%> (+0.07%)	⬆️
beets/importer/stages.py	89.44% <92.00%> (+0.69%)	⬆️
beets/importer/tasks.py	90.70% <81.48%> (-0.26%)	⬇️
beets/ui/commands/import_/session.py	55.14% <6.66%> (-3.19%)	⬇️

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.