feat: improve caching mechanism

[raphael0202]

This PR includes several commits that add a disk cache mechanism to cache images, remove the CachedStore class, and add tests for _get_image_from_url.

[codecov]

Codecov Report

Merging #1281 (233064d) into main (5e86341) will increase coverage by 0.12%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##             main    #1281      +/-   ##
==========================================
+ Coverage   56.49%   56.61%   +0.12%     
==========================================
  Files          77       77              
  Lines        7542     7547       +5     
==========================================
+ Hits         4261     4273      +12     
+ Misses       3281     3274       -7     

Files	Coverage Δ
...y/neural/keras_category_classifier_3_0/__init__.py	73.45% <ø> (ø)
robotoff/prediction/ocr/location.py	98.87% <100.00%> (ø)
robotoff/settings.py	92.05% <100.00%> (+0.05%)	⬆️
robotoff/utils/cache.py	100.00% <100.00%> (+15.00%)	⬆️
robotoff/prediction/ocr/packager_code.py	59.74% <80.00%> (ø)
robotoff/prediction/ocr/trace.py	40.62% <80.00%> (+1.91%)	⬆️
robotoff/app/api.py	48.59% <0.00%> (ø)
robotoff/images.py	37.07% <0.00%> (ø)
robotoff/utils/image.py	88.70% <87.50%> (+10.27%)	⬆️
robotoff/workers/tasks/import_image.py	29.59% <0.00%> (ø)

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