ENH: add message 1 decoding to nexrad level2 reader

[kmuehlbauer]

• Closes NEXRADLevel2 Reader Error for Older Files #256
• Tests added
• Changes are documented in history.md

[codecov]

Codecov Report

Attention: Patch coverage is 96.96970% with 2 lines in your changes missing coverage. Please review.

Project coverage is 93.57%. Comparing base (f5f1f6f) to head (96fd08c).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
xradar/io/backends/nexrad_level2.py	96.96%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #267      +/-   ##
==========================================
- Coverage   93.57%   93.57%   -0.01%     
==========================================
  Files          26       26              
  Lines        5042     5073      +31     
==========================================
+ Hits         4718     4747      +29     
- Misses        324      326       +2     

Flag	Coverage Δ
notebooktests	79.20% <80.30%> (+0.22%)	⬆️
unittests	93.15% <96.96%> (+<0.01%)	⬆️

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[kmuehlbauer]

Heads-up! This is working nicely. It was almost straightforward to implement (most of the structure was already defined). I'm going to merge tomorrow and let a release out, if no one beats me to it ;-)