[experimental] z support get_dims for shapes

[LucaMarconato]

Experimental support of z dimension for shapes.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review. :white_check_mark: Project coverage is 92.09%. Comparing base (8c3e518) to head (27e7e24).

Files with missing lines	Patch %	Lines
src/spatialdata/models/_utils.py	50.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #997      +/-   ##
==========================================
- Coverage   92.11%   92.09%   -0.02%     
==========================================
  Files          48       48              
  Lines        7440     7442       +2     
==========================================
+ Hits         6853     6854       +1     
- Misses        587      588       +1     

Files with missing lines	Coverage Δ
src/spatialdata/models/_utils.py	89.20% <50.00%> (-0.46%)	:arrow_down:

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