Maint sparseindex

[AhmetNSimsek]

TODO:

• create a data proxy folder for version 1 specifically
• regions should be fetchable without forming sparseindex. use sparse index for assignments only

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 40.74074% with 48 lines in your changes missing coverage. Please review.

Project coverage is 46.02%. Comparing base (dc63457) to head (d23a2b8).
Report is 32 commits behind head on main.

Files with missing lines	Patch %	Lines
siibra/volumes/sparsemap.py	41.53%	38 Missing ⚠️
siibra/retrieval/repositories.py	28.57%	5 Missing ⚠️
siibra/retrieval/requests.py	44.44%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #525      +/-   ##
==========================================
+ Coverage   46.00%   46.02%   +0.02%     
==========================================
  Files          75       75              
  Lines        7232     7165      -67     
==========================================
- Hits         3327     3298      -29     
+ Misses       3905     3867      -38     

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[xgui3783]

I have an issue with the name of the files and how decoders are found. Others looks solid.

[dickscheid]

I didn't check all code but it looks reasonable to me. once merged we need to test thoroughly that probabilistic assignment behaves identical to previous versions, especially using the tutorial notebooks that do assignment.