[python] Canned tests for old/new arrays without/with new shapes

[johnkerl]

Issue and/or context: As tracked on issue #2407 / [sc-51048].

Note that the intended Python and R API changes are all agreed on and finalized as described in #2407.

Changes:

Here we keep around an old-style experiment to regress on our ability to upgrade its shapes.

For this PR we only test accessors on the data. On #3148 these unit test will be extended to check their upgrading of the old-style experiment.

Notes for Reviewer:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.13%. Comparing base (46bf2ec) to head (880e26b).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3156      +/-   ##
==========================================
+ Coverage   82.92%   83.13%   +0.20%     
==========================================
  Files          50       50              
  Lines        5236     5247      +11     
==========================================
+ Hits         4342     4362      +20     
+ Misses        894      885       -9     

Flag	Coverage Δ
python	83.13% <ø> (+0.20%)	⬆️

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

Components	Coverage Δ
python_api	83.13% <100.00%> (+0.20%)	⬆️
libtiledbsoma	∅ <ø> (∅)

[johnkerl]

Thanks @nguyenv ! :)