Migrate to Rust edition 2021 #120

Job	Run time
Check #[cfg]s	11s
Style check	14s
Test tier1 (i686-unknown-linux-gnu, true, ubuntu-24.04)	3m 55s
Verify build (stable, ubuntu-24.04)	3m 31s
Test tier1 (x86_64-unknown-linux-gnu, true, ubuntu-24.04)	3m 26s
Verify build (stable, macos-14)	18s
Test tier1 (aarch64-apple-darwin, macos-14)	2m 2s
Verify build (stable, windows-2022)	4m 25s
Test tier1 (x86_64-pc-windows-gnu, windows-2022, 64, x86_64)	1m 54s
Verify build (nightly, ubuntu-24.04)	14m 54s
Test tier1 (x86_64-pc-windows-msvc, windows-2022)	3m 53s
Verify build (nightly, macos-14)	1m 1s
Test tier1 (i686-pc-windows-msvc, windows-2022)	4m 9s
Verify build (nightly, windows-2022)	3m 59s
Verify build (1.63.0, ubuntu-24.04)	5m 43s
Verify build (1.63.0, macos-14)	2m 7s
Verify build (1.63.0, windows-2022)	7m 13s
Verify build (beta, ubuntu-24.04)	3m 4s
Test tier2	0s
Test tier2 VM	0s
success	1s
	1h 6m 0s

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