chore: bump MSRV to 1.81 #2156

Job	Run time
check no_std	1m 3s
docs	58s
clippy	1m 11s
features stable	2m 31s
features stable --all-targets	3m 31s
fmt	16s
miri --no-default-features	5m 37s
features nightly	2m 25s
miri	5m 1s
features nightly --all-targets	3m 42s
test ubuntu-latest stable --no-default-features	1m 10s
wasm	44s
miri --all-features	7m 32s
test ubuntu-latest stable	1m 28s
test ubuntu-latest nightly --no-default-features	1m 18s
test ubuntu-latest nightly	1m 15s
test ubuntu-latest 1.81 --no-default-features	37s
test ubuntu-latest 1.81	38s
test windows-latest stable --no-default-features	3m 50s
test windows-latest stable	2m 56s
test windows-latest nightly --no-default-features	2m 56s
test windows-latest nightly	3m 15s
test windows-latest 1.81 --no-default-features	1m 49s
test windows-latest 1.81	1m 47s
test ubuntu-latest 1.81 --features json	41s
test windows-latest 1.81 --features json	2m 53s
test ubuntu-latest nightly --all-features	1m 24s
test windows-latest nightly --all-features	3m 16s
ci success	3s
	1h 5m 47s

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