bug: use find_spec for spatialpandas.dask import

[hoxbro]

Previous if some import failed in import spatialpandas.dask there was no way to see it. It was leading to weird behavior.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.47%. Comparing base (7aabfff) to head (c50d8d6).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #163      +/-   ##
==========================================
- Coverage   77.50%   77.47%   -0.03%     
==========================================
  Files          50       50              
  Lines        4845     4844       -1     
==========================================
- Hits         3755     3753       -2     
- Misses       1090     1091       +1     

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