[python] resolve MacOS CI OOM failure

[bkmartinjr]

Fixes SOMA-335

There has been a long-standing crash in the MacOS CI. The root cause was an OOM in tests caused by the 7GiB runner config. It occurred primarily in MacOS because max resident memory usage in MacOS is higher than Linux.

As part of this, also found a bug in ExperimentAxisQuery.to_anndata obsm/varm reading, where it would incorrectly determine the shape of the second (feature) dimension (this would only occur in cases where a feature had only zeros, and was therefore not written as part of the sparse array).

Changes:

• added a SOMATileDBContext fixture in the tests, with memory budget set to fairly small values when in the CI environment.
• used the new fixture in the tests which create memory pressure
• fixed aforementioned bug in ExperimentAxisQuery._read_inner_ndarray
• fixed formatting in several GHA yaml files

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.47%. Comparing base (606197d) to head (5cbba58).
Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #4148       +/-   ##
===========================================
+ Coverage   66.25%   89.47%   +23.21%     
===========================================
  Files         161       60      -101     
  Lines       19842     7165    -12677     
  Branches     1238        0     -1238     
===========================================
- Hits        13147     6411     -6736     
+ Misses       6287      754     -5533     
+ Partials      408        0      -408     

Flag	Coverage Δ
libtiledbsoma	?
python	89.47% <100.00%> (-0.03%)	⬇️

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Components	Coverage Δ
python_api	89.47% <100.00%> (-0.03%)	⬇️
libtiledbsoma	∅ <ø> (∅)

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