Update MSRV to 1.81 (#332) #626

Job	Run time
format	11s
Clippy	53s
cargo-build (aarch64-linux-android, ubuntu-22.04)	3m 1s
cargo-build (armv7-linux-androideabi, ubuntu-22.04)	3m 9s
cargo-test (ubuntu-22.04, default, stable)	3m 57s
cargo-build (i686-linux-android, ubuntu-22.04)	3m 5s
cargo-test (macos-13, default, stable)	7m 12s
cargo-build (x86_64-linux-android, ubuntu-22.04)	2m 54s
cargo-build (x86_64-unknown-linux-musl, ubuntu-22.04)	3m 0s
cargo-test (windows-2019, default, stable)	7m 1s
cargo-build (aarch64-apple-ios, macos-13)	4m 38s
cargo-test (ubuntu-22.04, beta)	5m 47s
cargo-test (ubuntu-22.04, blocking)	6m 1s
cargo-test (ubuntu-22.04, blocking,beta)	6m 17s
cargo-test (ubuntu-22.04, tls-rustls --no-default-features)	5m 35s
cargo-test (ubuntu-22.04, tls-vendored-openssl --no-default-features)	6m 23s
cargo-test (ubuntu-22.04, beta, default)	3m 55s
cargo-test (ubuntu-22.04, 1.81.0, default)	5m 33s
	1h 18m 32s

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