Beat unique fix

[TkTech]

It's possible for the celery beat scheduler to skip calling apply_async(), if it's unable to import the actual task. In these cases, it'll resort to using send_task(), see https://github.com/celery/celery/blob/main/celery/beat.py#L406. This means that our unique lock may never be checked, since we hook it into Task.apply_async().

This change adds verification of the lock at the time a task is run, while keeping the early lock as well.

This is a known issue with other similar libraries, see:

• Not working for scheduled tasks cameronmaske/celery-once#136
• Multiple tasks do not generate singleton locks steinitzu/celery-singleton#38

[codecov]

Codecov Report

Attention: 15 lines in your changes are missing coverage. Please review.

Comparison is base (43727fa) 58.74% compared to head (fbbcc5a) 60.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #6      +/-   ##
==========================================
+ Coverage   58.74%   60.00%   +1.25%     
==========================================
  Files           7        7              
  Lines         286      295       +9     
==========================================
+ Hits          168      177       +9     
  Misses        118      118              

Files	Coverage Δ
celery_heimdall/__init__.py	100.00% <100.00%> (ø)
celery_heimdall/config.py	100.00% <100.00%> (ø)
celery_heimdall/errors.py	100.00% <100.00%> (ø)
celery_heimdall/contrib/inspector/monitor.py	0.00% <0.00%> (ø)
celery_heimdall/contrib/inspector/cli.py	0.00% <0.00%> (ø)
celery_heimdall/task.py	93.79% <89.13%> (+0.41%)	⬆️
celery_heimdall/contrib/inspector/models.py	0.00% <0.00%> (ø)

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.