Improve variable naming

[thorbjoernl]

Change Summary

• Improved variable naming mainly in ExperimentOutput.
• Adds type hinting.
• Removes superfluous if check (EvalSetup no longer has var_mapping).
• Use namedtuple for tuple return types.

Related issue number

NA

Checklist

• Start with a draft-PR
• The PR title is a good summary of the changes
• PR is set to AeroTools and a tentative milestone
• Documentation reflects the changes where applicable
• Tests for the changes exist where applicable
• Tests pass locally
• Tests pass on CI
• At least 1 reviewer is selected
• Make PR ready to review

[codecov]

Codecov Report

Attention: Patch coverage is 95.83333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 79.31%. Comparing base (16208c7) to head (ac80b76).
Report is 491 commits behind head on main-dev.

Files with missing lines	Patch %	Lines
pyaerocom/aeroval/experiment_output.py	95.65%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           main-dev    #1194      +/-   ##
============================================
+ Coverage     79.26%   79.31%   +0.05%     
============================================
  Files           131      131              
  Lines         20239    20230       -9     
============================================
+ Hits          16042    16046       +4     
+ Misses         4197     4184      -13     

Flag	Coverage Δ
unittests	79.31% <95.83%> (+0.05%)	⬆️

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[lewisblake]

Looks good! This is a valuable update, thanks.