Implement file locking for Nexrad Level2 and IRIS/Sigmet backends

[kmuehlbauer]

• Closes NEXRAD issue - IndexError index out of bounds #207
• Tests added
• Changes are documented in history.md

[codecov]

Codecov Report

Attention: Patch coverage is 97.36842% with 1 line in your changes missing coverage. Please review.

Project coverage is 93.58%. Comparing base (fc43e60) to head (805012c).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
xradar/io/backends/nexrad_level2.py	96.29%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #269      +/-   ##
==========================================
+ Coverage   93.57%   93.58%   +0.01%     
==========================================
  Files          26       26              
  Lines        5073     5082       +9     
==========================================
+ Hits         4747     4756       +9     
  Misses        326      326              

Flag	Coverage Δ
notebooktests	79.24% <92.10%> (+0.03%)	⬆️
unittests	93.17% <97.36%> (+0.01%)	⬆️

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