[python] Carrara/tiledbv3 URI support

[bkmartinjr]

Changes:

• preliminary method to distinguish tiledb URI mode: absolute or relative (aka Carrara vs Cloud)
• add relative URI handling for tiledb URIs
• draft test cases - hard-coded against QA backend for now (must be manually executed outside of CI)

This PR also contains the following changes, which have been split out into #4286 and #4287:

• fix mis-use of Core group add API noticed during review
• fix bug in Collection._set_element that was adding every group member as a "Collection" (in the memory-cached collection, i.e., what the .members() method return).

Work not complete in this PR:

• port SOMATileDBContext.data_protocol to use the (not yet available) Core API to introspect Ctx state
• align SOMATileDBContext.data_protocol signature with TileDB-Py

[codecov]

Codecov Report

❌ Patch coverage is 87.34177% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.17%. Comparing base (41b04f2) to head (b2d2ec5).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4283      +/-   ##
==========================================
+ Coverage   86.85%   89.17%   +2.32%     
==========================================
  Files         137       62      -75     
  Lines       20705     7142   -13563     
  Branches       15        0      -15     
==========================================
- Hits        17983     6369   -11614     
+ Misses       2722      773    -1949     

Flag	Coverage Δ
python	89.17% <87.34%> (-0.06%)	⬇️
r	?

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

Components	Coverage Δ
python_api	89.17% <87.34%> (-0.06%)	⬇️
libtiledbsoma	∅ <ø> (∅)

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