Fixing bug updating the detection id while running more than one day

[adybbroe]

This PR should solve a bug found in the recently introduce addition to include a unique detection id.
The initialization was always reading from the cache file, and thus the date was never updated.

• Closes #xxxx
• Tests added
• Tests passed: Passes pytest
• Passes flake8
• Fully documented

[mraspaud]

Nice with the new tests! some comments.

[codecov-commenter]

Codecov Report

Merging #20 (582f71c) into main (fcc586c) will increase coverage by 0.17%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main      #20      +/-   ##
==========================================
+ Coverage   82.55%   82.73%   +0.17%     
==========================================
  Files          21       21              
  Lines        2540     2554      +14     
  Branches      379      386       +7     
==========================================
+ Hits         2097     2113      +16     
+ Misses        412      410       -2     
  Partials       31       31              

Flag	Coverage Δ
unittests	82.73% <100.00%> (+0.17%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
activefires_pp/post_processing.py	66.21% <100.00%> (+0.22%)	⬆️
activefires_pp/tests/conftest.py	96.22% <100.00%> (+1.86%)	⬆️
...efires_pp/tests/test_fire_detection_id_handling.py	100.00% <100.00%> (ø)

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[coveralls]

coverage: 83.947% (+0.2%) from 83.78%
when pulling 81635c8 on fix-bug-detection-id
into fcc586c on main.

[adybbroe]

Are you okay with this now @mraspaud Can we merge?

[mraspaud]

LGTM