[UPGRADE] of station controller. Allowing for faster and more stable run.

[vogt31337]

The station controller adjusts the reactive power of a group of generation units ("a station") until a
measured quantity reaches a set point. It supports reactive power control (Q_ctrl), voltage
control (V_ctrl), power factor control (PF_ctrl_ind / PF_ctrl_cap), tan_phi_ctrl
and droop variants of the Q and V control modi, mirroring the station controllers known from
PowerFactory.

It now allows to control many stations at once (tested with N=500), in multi station mode, the droop is now evaluated inside the station residual, so there is only one loop. An additional update_method is implemented based on the jacobian / sensitivity, and the convergence is improved.

The timing shows an improvement factor of ~22 and the number of powerflows is reduced, backward compatibility is given and mixed operations is possible.

More details in doc/control/station_control.rst

[codecov]

Codecov Report

❌ Patch coverage is 83.56808% with 105 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.97%. Comparing base (1576fe6) to head (c7ba4e6).
⚠️ Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
pandapower/control/controller/station_control.py	83.02%	100 Missing ⚠️
pandapower/control/util/sensitivity.py	89.79%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3057      +/-   ##
===========================================
+ Coverage    71.67%   71.97%   +0.29%     
===========================================
  Files          355      356       +1     
  Lines        39348    39887     +539     
===========================================
+ Hits         28204    28707     +503     
- Misses       11144    11180      +36     

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[sonarqubecloud]

Quality Gate failed

Failed conditions
C Reliability Rating on New Code (required ≥ A)
C Security Rating on New Code (required ≥ A)

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