Refactor HRIT/LRIT format reader.

[sbrodehl]

Refactor HRIT/LRIT format reader code, as mentioned in #2076 .

• Add your name to AUTHORS.md if not there already

[codecov]

Codecov Report

Merging #2087 (c1d469b) into main (dd77305) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2087   +/-   ##
=======================================
  Coverage   93.89%   93.90%           
=======================================
  Files         283      283           
  Lines       42537    42543    +6     
=======================================
+ Hits        39942    39948    +6     
  Misses       2595     2595           

Flag	Coverage Δ
behaviourtests	4.71% <0.00%> (-0.01%)	⬇️
unittests	94.46% <100.00%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
satpy/readers/hrit_base.py	83.06% <100.00%> (+0.57%)	⬆️

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[coveralls]

Coverage increased (+0.0008%) to 94.399% when pulling c1d469b on sbrodehl:dev-hrit-base-refactor into dd77305 on pytroll:main.

[mraspaud]

LGTM, thanks for taking the time, it's much cleaner indeed!

[sfinkens]

Awesome, thanks a lot for taking the time!