Spotify: Improve 503 error handling

[arsaboo]

Spotify currently crashes out on 503 errors.

spotify: Service Unavailable.
Traceback (most recent call last):
  File "/home/arsaboo/.local/lib/python3.10/site-packages/beetsplug/spotify.py", line 244, in _handle_response
    response.raise_for_status()
  File "/home/arsaboo/.local/lib/python3.10/site-packages/requests/models.py", line 1167, in raise_for_status
    raise HTTPError(http_error_msg, response=self)
requests.exceptions.HTTPError: 503 Server Error: Service Unavailable for url: https://api.spotify.com/v1/tracks?ids=7ElISEDbwXtbB4xAvFRLqb%2C1DgdyYtZjfmBOxLuDLHXyH%2C0AeK8BB9Kk7qxyUgCfEwLO%2C6SJyEptZ7MiFJYe9FUbk7Q%2C5C9GZT725aQAdUT97hjaiO%2C0nGkSdNwjPh0tpqQU0FCCR%2C7EsWEd2s6hUUNw3I2QqKrn%2C3LfDSh8oDROFmebWrUq7De%2C036co96fRtoFd8n7pvklci%2C72sBOZVBWsfgKRWAF61jDA%2C3T6PwNpROC4WkWvrnqIcCJ%2C1USz6iqnhAnfHCcnjylrLa%2C7w6sxU9PQT8nJYzqGswOvM%2C4KeexCKGpjkBJS633QgxS2%2C0JuHzqHYYrauekCOUx4RrY%2C5cumiCqwlT9GAg2uktOZlg%2C2GbA6HFXqOGndhpPg42ifK%2C55nrl1ScrRDCv1ORLoEMlG%2C3YwLux5noWLxHhhE3OdIHS%2C1lCRbQsiWmNQUUSGYNvGT8

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/arsaboo/.local/bin/beet", line 6, in <module>
    sys.exit(main())
  File "/home/arsaboo/.local/lib/python3.10/site-packages/beets/ui/__init__.py", line 962, in main
    _raw_main(args)
  File "/home/arsaboo/.local/lib/python3.10/site-packages/beets/ui/__init__.py", line 903, in _raw_main
    subcommand.func(lib, suboptions, subargs)
  File "/home/arsaboo/.local/lib/python3.10/site-packages/beetsplug/spotify.py", line 570, in func
    self._fetch_info(lib, items, ui.should_write(), opts.force_refetch)
  File "/home/arsaboo/.local/lib/python3.10/site-packages/beetsplug/spotify.py", line 844, in _fetch_info
    track_details_by_id = self.get_track_details_by_id(unique_track_ids)
  File "/home/arsaboo/.local/lib/python3.10/site-packages/beetsplug/spotify.py", line 753, in get_track_details_by_id
    track_data = self._handle_response(
  File "/home/arsaboo/.local/lib/python3.10/site-packages/beetsplug/spotify.py", line 294, in _handle_response
    raise APIError("Service Unavailable.")
beetsplug.spotify.APIError: Service Unavailable.

This PR adds a retry mechanism that Spotify recommends for transient 503 errors.

To Do

• Changelog. (Add an entry to docs/changelog.rst to the bottom of one of the lists near the top of the document.)

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.62%. Comparing base (4782acb) to head (cad27b5).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
beetsplug/spotify.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6871      +/-   ##
==========================================
- Coverage   75.64%   75.62%   -0.03%     
==========================================
  Files         163      163              
  Lines       21317    21318       +1     
  Branches     3361     3361              
==========================================
- Hits        16126    16122       -4     
- Misses       4402     4405       +3     
- Partials      789      791       +2     

Files with missing lines	Coverage Δ
beetsplug/spotify.py	63.29% <0.00%> (-0.17%)	⬇️

... and 2 files with indirect coverage changes

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