Avoid bottlenecks in variable matching (#4178) #16865

Job	Run time
doctest (1.10, ubuntu-latest)	31m 9s
doctest (1.11-nightly, ubuntu-latest)	31m 55s
doctest (nightly, ubuntu-latest)	30m 7s
doctest (1.10, ubuntu-latest, depwarn=error)	31m 15s
doctest (1.10, macOS, RPTU)	15m 40s
test (1.6, short, ubuntu-latest)	1h 32m 12s
test (1.6, long, ubuntu-latest)	57m 27s
test (1.10, short, ubuntu-latest)	1h 12m 40s
test (1.10, long, ubuntu-latest)	46m 3s
test (1.11-nightly, short, ubuntu-latest)	1h 24m 8s
test (1.11-nightly, long, ubuntu-latest)	51m 37s
test (nightly, short, ubuntu-latest)	1h 27m 47s
test (nightly, long, ubuntu-latest)	51m 28s
test (1.10, short, ubuntu-latest, depwarn=error)	1h 9m 25s
test (1.10, long, ubuntu-latest, depwarn=error)	45m 31s
test (1.10, short, macOS, RPTU)	13m 56s
test (1.10, long, macOS, RPTU)	14m 19s
test (1.10, book, ubuntu-latest)	53m 12s
test (nightly, book, ubuntu-latest)	1h 4m 14s
	15h 44m 5s

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