FIX: do not apply scale/offset in datamet reader, leave it to xarray instead

[kmuehlbauer]

• Closes #xxxx
• Tests added
• Changes are documented in history.md

[codecov]

Codecov Report

Attention: Patch coverage is 55.55556% with 4 lines in your changes missing coverage. Please review.

Project coverage is 91.97%. Comparing base (34a9e82) to head (53445da).
Report is 25 commits behind head on main.

Files with missing lines	Patch %	Lines
xradar/io/backends/datamet.py	55.55%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #209      +/-   ##
==========================================
- Coverage   91.98%   91.97%   -0.01%     
==========================================
  Files          23       23              
  Lines        4541     4538       -3     
==========================================
- Hits         4177     4174       -3     
  Misses        364      364              

Flag	Coverage Δ
notebooktests	78.25% <0.00%> (+0.05%)	⬆️
unittests	90.23% <55.55%> (-0.01%)	⬇️

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