[python] Additional experiment-query unit tests

[bkmartinjr]

Issue and/or context:

#778 - need to increase unit tests

Changes:

Added additional unit tests for somacore.ExperimentAxisQuery and related.

Notes for Reviewer:

Note: routines in _fast_csr compiled by numba are tested, but codecov will not report them as such

[codecov-commenter]

Codecov Report

Base: 74.94% // Head: 88.69% // Increases project coverage by +13.75% 🎉

Coverage data is based on head (63e6284) compared to base (b3d7581).
Patch has no changes to coverable lines.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #789       +/-   ##
===========================================
+ Coverage   74.94%   88.69%   +13.75%     
===========================================
  Files          70       30       -40     
  Lines        3372     1796     -1576     
===========================================
- Hits         2527     1593      -934     
+ Misses        845      203      -642     

Flag	Coverage Δ
python	88.69% <ø> (-0.23%)	⬇️
r	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
apis/python/src/tiledbsoma/collection.py	90.17% <0.00%> (-1.74%)	⬇️
apis/python/src/tiledbsoma/sparse_nd_array.py	94.06% <0.00%> (-0.85%)	⬇️
R/TileDBObject.R
R/utils.R
src/include/tiledbsoma/column_buffer.h
inst/tiledb/include/tiledb/deleter.h
R/SOMACollectionBase.R
R/SOMADenseNdArray.R
src/include/span/span.hpp
src/include/tiledbsoma/array_buffers.h
... and 32 more

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[johnkerl]

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