FIX: implement more robust angle_res retrieval

[kmuehlbauer]

• [x] Closes #112
• [x] Tests added
• [x] Changes are documented in history.md

[codecov[bot]]

Codecov Report

Merging #118 (4660b50) into main (e464ac7) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #118   +/-   ##
=======================================
  Coverage   88.17%   88.18%           
=======================================
  Files          19       19           
  Lines        3333     3335    +2     
=======================================
+ Hits         2939     2941    +2     
  Misses        394      394           

Flag	Coverage Δ
unittests	88.18% <100.00%> (+<0.01%)	:arrow_up:

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Impacted Files	Coverage Δ
xradar/util.py	97.31% <100.00%> (+0.03%)	:arrow_up: