Fix compression and serializer encodings

[BrianMichell]

ZFP is an array to bytes serializer and cannot be treated as a compressor directly. Changes here make that distinction opaque to the user. Also avoids creating an unnecessary default compressor on ZFP compressed stores.

[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.30%. Comparing base (c3ba558) to head (b512c36).
⚠️ Report is 217 commits behind head on main.

Files with missing lines	Patch %	Lines
src/mdio/builder/xarray_builder.py	65.21%	6 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #748      +/-   ##
==========================================
+ Coverage   85.30%   88.30%   +2.99%     
==========================================
  Files          46       90      +44     
  Lines        2219     4952    +2733     
  Branches      306      326      +20     
==========================================
+ Hits         1893     4373    +2480     
- Misses        281      504     +223     
- Partials       45       75      +30     

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[BrianMichell]

In order to append additional Variables to the Dataset (e.g. transpose volume) in Zarr V2 I had to add the following snippet right before calling to_mdio.

This should be less of an issue with this PR and something that should be addressed in the MDIO API.

    for var_name in list(ds.data_vars) + list(ds.coords):
        if "_FillValue" in ds[var_name].attrs:
            del ds[var_name].attrs["_FillValue"]

[rhardisty]

I was looking through test_dataset_serializer.py and I only found imports for zfpy.ZFPY. Are there tests for zarr.codecs.numcodecs.ZFPY?

[BrianMichell]

#747 will help with this. Lossy compression has not been a high priority.

[rhardisty]

Oh nice. You're on it already.