Update README.md to use LazyLock instead of OnceCell #2597

Job	Run time
rustfmt	9s
miri-regex-automata	16m 4s
test (stable, ubuntu-latest, stable)	3m 38s
msrv	2m 31s
test (stable-32, ubuntu-latest, stable, i686-unknown-linux-gnu)	2m 38s
testfull-regex	3m 25s
testfull-regex-automata	8m 18s
test (stable-powerpc64, ubuntu-latest, stable, powerpc64-unknown-linux-gnu)	7m 58s
test (stable-s390x, ubuntu-latest, stable, s390x-unknown-linux-gnu)	9m 38s
testfull-regex-capi	20s
test (beta, ubuntu-latest, beta)	3m 28s
testfull-regex-syntax	1m 47s
test (nightly, ubuntu-latest, nightly)	2m 51s
test (macos, macos-latest, stable)	2m 45s
test (win-msvc, windows-latest, stable)	6m 11s
test (win-gnu, windows-latest, stable-x86_64-gnu)	3m 18s
	1h 14m 59s

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