Faster `find_position` #676

Job	Run time
test	54s
check format	6s
msrv	36s
check	19s
check (--no-default-features)	9s
check (--no-default-features --features use_alloc)	7s
check (--all-targets --all-features)	25s
All checks succeeded	1s
	2m 37s

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