Only enable cache on request

[stefanv]

This PR disables the cache by default, but enables it when the --cache flag is specified.

Closes #89

[codecov-commenter]

Codecov Report

Merging #91 (5253719) into main (929eda0) will increase coverage by 1.38%. The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main      #91      +/-   ##
==========================================
+ Coverage   61.45%   62.83%   +1.38%     
==========================================
  Files           7        7              
  Lines         550      522      -28     
==========================================
- Hits          338      328      -10     
+ Misses        212      194      -18     

Impacted Files	Coverage Δ
pipeline.py	51.53% <0.00%> (-1.88%)	:arrow_down:
mothra/binarization.py	73.43% <100.00%> (-0.41%)	:arrow_down:
mothra/cache.py	100.00% <100.00%> (ø)
mothra/measurement.py	71.15% <100.00%> (-0.55%)	:arrow_down:
mothra/ruler_detection.py	77.63% <100.00%> (-0.30%)	:arrow_down:
mothra/tracing.py	63.09% <100.00%> (-0.44%)	:arrow_down:
mothra/identification.py

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[alexdesiqueira]

Thank you Stéfan!