Support nodata values

[banesullivan]

Potential solution to #34

It's a bit dirty as it modifies the data in place or creates a copy of the integer data to float dtype (potentially expensive).

This is my first pass at this, but I'd like to look into some other ways of going about this that do not have as bad of side effects

cc @giswqs

[codecov-commenter]

Codecov Report

Merging #35 (0101820) into main (e19eab1) will decrease coverage by 3.85%.
The diff coverage is 52.17%.

@@            Coverage Diff             @@
##             main      #35      +/-   ##
==========================================
- Coverage   90.73%   86.87%   -3.86%     
==========================================
  Files           8        8              
  Lines         205      221      +16     
==========================================
+ Hits          186      192       +6     
- Misses         19       29      +10     

Impacted Files	Coverage Δ
pvxarray/accessor.py	80.64% <42.10%> (-15.19%)	⬇️
pvxarray/errors.py	100.00% <100.00%> (ø)
pvxarray/rectilinear.py	97.05% <100.00%> (ø)
pvxarray/structured.py	85.29% <100.00%> (ø)

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