reduces var to only unique, returns totnum in _len_datapoints

[dulte]

Change Summary

Something made the earlinet eval super slow. Some debugging lead me to ungriddeddata._len_datapoints.

1. the var list has many thousands of copies of the same var. I guess this is an error? Made it so var = list(set(var)). The resulting totnum is drastically different
2. totnum was not actually returned

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.49%. Comparing base (2abd82e) to head (f871ce6).
⚠️ Report is 149 commits behind head on main-dev.

Additional details and impacted files

@@             Coverage Diff              @@
##           main-dev    #1788      +/-   ##
============================================
+ Coverage     78.36%   78.49%   +0.12%     
============================================
  Files           176      176              
  Lines         23414    23446      +32     
============================================
+ Hits          18349    18404      +55     
+ Misses         5065     5042      -23     

Flag	Coverage Δ
unittests	78.49% <100.00%> (+0.12%)	⬆️

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