perf: Avoid re-canonicalizing the entire IntervalSet on push #2927

Job	Run time
msrv	4m 9s
testfull-regex	2m 40s
testfull-regex-capi	22s
testfull-regex-automata	7m 20s
miri-regex-automata	11m 23s
rustfmt	7s
docsrs	30s
testfull-regex-syntax	1m 52s
test (win-gnu, windows-latest, stable-x86_64-gnu)	3m 27s
test (nightly, ubuntu-latest, nightly)	2m 51s
test (stable, ubuntu-latest, stable)	2m 42s
cross (powerpc64-unknown-linux-gnu)	2m 15s
test (beta, ubuntu-latest, beta)	2m 49s
cross (aarch64-unknown-linux-gnu)	2m 5s
cross (powerpc-unknown-linux-gnu)	2m 10s
test (win-msvc, windows-latest, stable)	5m 56s
cross (s390x-unknown-linux-gnu)	2m 12s
cross (i686-unknown-linux-gnu)	1m 57s
test (macos, macos-latest, stable)	3m 0s
	59m 47s

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