TPC space-charge: Improve GEM frame charging-up distortions

[matthias-kleiner]

Adding:

• downsampling of space-charge objects
• simulation of n-sectors only
• some helper functions
• weighted filling of charging-up of GEM frames for smoother potential
• set global distortions from function

[github-actions[bot]]

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[alibuild]

Error while checking build/O2/fullCI_slc9 for a2183b141f43723330bc1202b927b1fbd20f4dda at 2025-12-13 14:58:

## sw/BUILD/o2checkcode-latest/log
--
========== List of errors found ==========
++ GRERR=0
++ grep -v clang-diagnostic-error error-log.txt
++ grep ' error:'
++ GRERR=1
++ [[ 1 == 0 ]]
++ mkdir -p /sw/INSTALLROOT/809088166d9118c2290378e8314a2e0a282b00d7/slc9_x86-64/o2checkcode/1.0-local162/etc/modulefiles
++ cat
--

Full log here.