update(Mf6Splitter): change how node mapping is stored and loaded

[jlarsen-usgs]

• save_node_mapping now writes a compressed hdf5 file and stores additional modelgrid reconstruction information for original and split model representations
• load_node_mapping changed to a static method that returns a Mf6Splitter object that can be used for array reconstruction
• updated autotests
• added example usage to mf6_parallel_model_splitting_example.py
• json node mapping files no longer supported, user must rewrite node mapping files as hdf5 files.
• bugfix for observation file naming convention on remapped obs files

[jlarsen-usgs]

@mjr-deltares, here are the updates to the model splitter for more efficient storage and loading of the "node mapping" files. If you'd like to give them a test, usage is as follows

mfs = Mf6Splitter(my_sim)
new_sim = mfs.split_model(array)

node_map_file = "my_node_map.h5"
mfs.save_node_mapping(node_map_file)

mfs2 = Mf6Splitter.load_node_mapping(node_map_file)

I tested this on the average annual long island model and HDF5 file processing and write time was ~5 seconds, read and reconstruction time was ~1.5 seconds, and HDF5 file size was about 63 MB, which includes information to reconstruct the original and split model grids, and the mappings to link these together.

[codecov]

Codecov Report

Attention: Patch coverage is 96.84211% with 6 lines in your changes missing coverage. Please review.

Project coverage is 74.3%. Comparing base (bb9824e) to head (e583173).
Report is 64 commits behind head on develop.

Files with missing lines	Patch %	Lines
flopy/mf6/utils/model_splitter.py	96.8%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #2465     +/-   ##
=========================================
+ Coverage     68.4%   74.3%   +5.8%     
=========================================
  Files          294     293      -1     
  Lines        59390   62092   +2702     
=========================================
+ Hits         40652   46135   +5483     
+ Misses       18738   15957   -2781     

Files with missing lines	Coverage Δ
flopy/mf6/utils/output_util.py	74.4% <100.0%> (+2.0%)	⬆️
flopy/mf6/utils/model_splitter.py	73.8% <96.8%> (+15.1%)	⬆️

... and 251 files with indirect coverage changes

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