Additional fixes

[mmagnuski]

• fix pylabianca.utils.assign_session_coord() when the passed xarray.DataArray has the 'cell' dimension in .coords but not in .dims (for example after doing arr.isel(cell=2))
• make sure pln.aggregate() works when the zscore is passed as an xarray
• FIX: dict_to_xarray would fail for dicts with xarrays without trial dimension

TODOs:

• make sure the is test for the zscore as xarray in aggregate
• check what happens now (vs what should happen) when aggregate is given a dictionary and an xarray zscore (should get two dictionaries most likely).
• add deprecations to xarray_to_dict and dict_to_xarray for ses_name -> ses_coord
• add changes to whatsnew

[codecov]

Codecov Report

❌ Patch coverage is 93.33333% with 2 lines in your changes missing coverage. Please review.

@@          Coverage Diff          @@
##            main     #61   +/-   ##
=====================================
  Coverage   77.9%   78.0%           
=====================================
  Files         19      19           
  Lines       3912    3922   +10     
=====================================
+ Hits        3050    3061   +11     
+ Misses       862     861    -1     

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