fix: citation, relational query index

[LucaMarconato]

• Fixed citation to Nature Methods paper
• Fixed index of partitioned dataframe for internal API used in the join operations

Skipped:

• Test against Python 3.12 (should fix the problem observed here https://github.com/vitessce/vitessce-python/actions/runs/9223316947/job/25376264495?pr=333). I will do this in this other PR: Removed dask pinning #570

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.55%. Comparing base (2a38051) to head (dbdbd7f).
Report is 83 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #569   +/-   ##
=======================================
  Coverage   92.55%   92.55%           
=======================================
  Files          42       42           
  Lines        6001     6003    +2     
=======================================
+ Hits         5554     5556    +2     
  Misses        447      447           

Files	Coverage Δ
src/spatialdata/_core/query/relational_query.py	95.51% <100.00%> (+0.02%)	⬆️
src/spatialdata/dataloader/datasets.py	90.68% <ø> (ø)

[LucaMarconato]

We are now testing against the minimum and maximum supported versions of Python: 3.9 and 3.12.

[LucaMarconato]

The test fails because of an error in dask that I guess is fixed in the latest version. We should remove the pinning for dask; I'll work on it here: #570.