Spatial cluster refactor

[FabianHofmann]

• The spatial clustering module was refactored. The changes lead to performance improvements and a more consistent clustering API.
  • The network object has a new accessor cluster which allows accessing clustering routines from the network itself. For example, n.cluster.cluster_spatially_by_kmeans returns a spatially clustered version of the network.
  • The default clustering strategies were refined. Per default, columns like efficiency and p_max_pu are now aggregated by the capacity weighted mean.
  • The clustering module now applies the custom strategies to time-dependant data.
  • Breaking change: The Clustering class no longer contains a positive and negative linemap.

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Unit tests for new features were added (if applicable).
• Newly introduced dependencies are added to environment.yaml, environment_docs.yaml and setup.py (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.

[codecov]

Codecov Report

Patch coverage: 85.85% and project coverage change: +1.04 🎉

Comparison is base (ee13f0b) 77.42% compared to head (c41e5ec) 78.47%.

❗ Current head c41e5ec differs from pull request most recent head 881b46f. Consider uploading reports for the commit 881b46f to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #673      +/-   ##
==========================================
+ Coverage   77.42%   78.47%   +1.04%     
==========================================
  Files          27       28       +1     
  Lines        6699     6691       -8     
  Branches     1424     1398      -26     
==========================================
+ Hits         5187     5251      +64     
+ Misses       1208     1136      -72     
  Partials      304      304              

Impacted Files	Coverage Δ
pypsa/clustering/__init__.py	82.75% <81.48%> (-17.25%)	⬇️
pypsa/clustering/spatial.py	70.00% <86.36%> (+26.82%)	⬆️
pypsa/components.py	78.11% <100.00%> (ø)

... and 7 files with indirect coverage changes

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[fneum]

LGTM, provided that test with PyPSA-Eur checks out!

Is test/test_networkclustering_module.py still needed or obsolete now?

[FabianHofmann]

Double-checked against pypsa-eur