Update of TPC fast space charge correction with splines

[davidrohr]

Rebased version of #14723

[github-actions[bot]]

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[alibuild]

Error while checking build/O2/fullCI_slc9 for dc97a9dbfb71e41b321757e02250bcb37ba30884 at 2025-12-15 11:27:

## sw/BUILD/O2-latest/log
/sw/SOURCES/O2/14921-slc9_x86-64/0/GPU/GPUTracking/Merger/GPUTPCGMTrackParam.cxx:525:270: error: no matching function for call to 'o2::gpu::TPCFastTransform::convVertexTimeToZOffset(int32_t&, float&, const int32_t&) const'
ninja: build stopped: subcommand failed.

Full log here.

[davidrohr]

Dataflow issue is independent, and compiles and runs on GPU, but should not be merged yet. Will comment more in the mail thread.