Migrate to Rust edition 2021 #121

Job	Run time
Check #[cfg]s	10s
Style check	17s
Test tier1 (i686-unknown-linux-gnu, true, ubuntu-24.04)	4m 22s
Verify build (stable, ubuntu-24.04)	3m 13s
Test tier1 (x86_64-unknown-linux-gnu, true, ubuntu-24.04)	3m 26s
Verify build (stable, macos-14)	19s
Test tier1 (aarch64-apple-darwin, macos-14)	1m 14s
Verify build (stable, windows-2022)	5m 38s
Test tier1 (x86_64-pc-windows-gnu, windows-2022, 64, x86_64)	1m 57s
Verify build (nightly, ubuntu-24.04)	15m 18s
Test tier1 (x86_64-pc-windows-msvc, windows-2022)	5m 0s
Verify build (nightly, macos-14)	1m 7s
Test tier1 (i686-pc-windows-msvc, windows-2022)	4m 22s
Verify build (nightly, windows-2022)	3m 6s
Verify build (1.63.0, ubuntu-24.04)	5m 31s
Verify build (1.63.0, macos-14)	2m 1s
Verify build (1.63.0, windows-2022)	6m 46s
Verify build (beta, ubuntu-24.04)	3m 6s
Test tier2	0s
Test tier2 VM	0s
success	1s
	1h 6m 54s

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