Stabilisers of timelike vectors, some refactoring for K3Auto.jl #18547

Job	Run time
extra-long-test	0s
doctest (1.10, Linux, RPTU, normal-memory)	28m 50s
doctest (1.11, Linux, RPTU, normal-memory)	25m 44s
doctest (nightly, Linux, RPTU, normal-memory)	32m 14s
test (1.6, short, Linux)	20m 45s
doctest (1.10, Linux, RPTU, normal-memory, depwarn=error)	27m 21s
test (1.6, long, Linux)	20m 11s
doctest (1.10, macOS, RPTU)	17m 43s
test (1.10, short, Linux)	21m 6s
test (1.10, long, Linux)	18m 45s
test (1.11, short, Linux)	19m 36s
test (1.11, long, Linux)	15m 40s
test (nightly, short, Linux)	2h 30m 19s
test (nightly, long, Linux)	22m 17s
test (1.10, short, Linux, RPTU, high-memory, depwarn=error)	18m 58s
test (1.10, long, Linux, RPTU, normal-memory, depwarn=error)	20m 2s
test (1.10, short, macOS, RPTU)	13m 55s
test (1.10, long, macOS, RPTU)	12m 13s
test (1.10, book, Linux, RPTU, normal-memory)	38m 2s
test (nightly, book, Linux, RPTU, normal-memory)	38m 16s
	9h 21m 57s

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