[WIP] Naive off-axis slice attempt for spherical-ish geometry #7462

Job	Run time
unit tests: py3.12 on macos-latest (pytest)	28m 9s
unit tests: py3.12 on ubuntu-latest (pytest)	14m 24s
answer tests: py3.9 on ubuntu-latest (nose)	12m 50s
unit tests: py3.9 on ubuntu-latest (nose)	12m 36s
unit tests: py3.9 on ubuntu-latest (pytest)	7m 30s
unit tests: py3.x on ubuntu-latest (pytest)	7m 32s
Image tests	6m 8s
unit tests: py3.12 on windows-latest (pytest)	18m 22s
	1h 47m 31s

Provide feedback