[WIP] Allow 3D process variables #11660

Job	Run time
Doctests (ubuntu-latest / Python 3.11)	4m 2s
Example scripts (ubuntu-latest / Python 3.12)	6m 30s
Example notebooks (ubuntu-latest / Python 3.12)	13m 27s
Tests (ubuntu-latest / Python 3.9)	7m 9s
Tests (ubuntu-latest / Python 3.10)	7m 21s
style	23s
Tests (ubuntu-latest / Python 3.11)	5m 51s
Tests (ubuntu-latest / Python 3.12)	12m 13s
Tests (macos-13 / Python 3.9)	5m 46s
Tests (macos-13 / Python 3.10)	7m 23s
Tests (macos-13 / Python 3.11)	6m 1s
Tests (macos-13 / Python 3.12)	6m 37s
Tests (macos-14 / Python 3.9)	4m 53s
Tests (macos-14 / Python 3.10)	5m 5s
Tests (macos-14 / Python 3.11)	3m 49s
Tests (macos-14 / Python 3.12)	4m 4s
Tests (windows-latest / Python 3.9)	13m 34s
Tests (windows-latest / Python 3.10)	7m 59s
Tests (windows-latest / Python 3.11)	7m 8s
Tests (windows-latest / Python 3.12)	7m 46s
	2h 17m 1s

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