chore: bump MSRV to 1.81 #2180

Job	Run time
features stable	2m 29s
docs	55s
features stable --all-targets	3m 32s
clippy	1m 8s
check no_std	53s
features nightly	2m 27s
fmt	14s
miri --no-default-features	5m 8s
features nightly --all-targets	3m 44s
miri	5m 7s
miri --all-features	7m 34s
test ubuntu-latest stable --no-default-features	1m 27s
wasm	46s
test ubuntu-latest stable	1m 27s
test ubuntu-latest nightly --no-default-features	1m 24s
test ubuntu-latest nightly	1m 18s
test ubuntu-latest 1.81 --no-default-features	40s
test ubuntu-latest 1.81	36s
test windows-latest stable --no-default-features	2m 45s
test windows-latest stable	2m 44s
test windows-latest nightly --no-default-features	2m 50s
test windows-latest nightly	2m 39s
test windows-latest 1.81 --no-default-features	1m 36s
test windows-latest 1.81	1m 23s
test ubuntu-latest 1.81 --features json	43s
test windows-latest 1.81 --features json	1m 21s
test ubuntu-latest nightly --all-features	1m 27s
test windows-latest nightly --all-features	3m 29s
ci success	1s
	1h 1m 47s

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