Feature: Support for dynamic worker args

[Nusnus]

Added default_worker_command fixture to allow configuring the worker’s cmdline without touching the docker stuff.
Added test shows example for changing the —pool configuration.

Requires adding command=fxtr("default_worker_command”) to all default worker containers overrides, everywhere!

[codecov]

Codecov Report

Attention: 13 lines in your changes are missing coverage. Please review.

Comparison is base (5b5ca39) 28.36% compared to head (ef975d1) 28.01%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
src/pytest_celery/vendors/worker/container.py	0.00%	4 Missing ⚠️
...rc/pytest_celery/vendors/redis/backend/fixtures.py	0.00%	3 Missing ⚠️
src/pytest_celery/vendors/redis/broker/fixtures.py	0.00%	3 Missing ⚠️
src/pytest_celery/vendors/worker/fixtures.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #203      +/-   ##
==========================================
- Coverage   28.36%   28.01%   -0.36%     
==========================================
  Files          36       36              
  Lines        1040     1053      +13     
  Branches      209      213       +4     
==========================================
  Hits          295      295              
- Misses        717      730      +13     
  Partials       28       28              

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[Nusnus]

Examples are expected to break as they install pytest-celery from main