Stabilisers of timelike vectors, some refactoring for K3Auto.jl #18546

Job	Run time
extra-long-test	0s
doctest (1.10, Linux, RPTU, normal-memory)	26m 59s
doctest (1.11, Linux, RPTU, normal-memory)	26m 10s
test (1.6, short, Linux)	12m 31s
doctest (nightly, Linux, RPTU, normal-memory)	5m 40s
test (1.6, long, Linux)	17m 5s
doctest (1.10, Linux, RPTU, normal-memory, depwarn=error)	28m 4s
test (1.10, short, Linux)	11m 45s
doctest (1.10, macOS, RPTU)	17m 22s
test (1.10, long, Linux)	14m 23s
test (1.11, short, Linux)	20m 17s
test (1.11, long, Linux)	11m 30s
test (nightly, short, Linux)	6m 56s
test (nightly, long, Linux)	2m 11s
test (1.10, short, Linux, RPTU, high-memory, depwarn=error)	11m 43s
test (1.10, long, Linux, RPTU, normal-memory, depwarn=error)	14m 34s
test (1.10, short, macOS, RPTU)	8m 39s
test (1.10, long, macOS, RPTU)	10m 18s
test (1.10, book, Linux, RPTU, normal-memory)	32m 33s
test (nightly, book, Linux, RPTU, normal-memory)	7m 0s
	4h 45m 40s

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