use datasets of the spaces if templates don't have any specified

[AhmetNSimsek]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 50.27%. Comparing base (5a0e6b3) to head (a130272).
Report is 443 commits behind head on main.

Files	Patch %	Lines
siibra/core/space.py	75.00%	1 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff             @@
##             main     #578       +/-   ##
===========================================
+ Coverage   36.81%   50.27%   +13.45%     
===========================================
  Files          61       69        +8     
  Lines        5421     6711     +1290     
===========================================
+ Hits         1996     3374     +1378     
+ Misses       3425     3337       -88     

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