make all methods `const` that can be `const` on 1.70.0 #1557

Job	Run time
cargo fmt	11s
Cross-compile (ubuntu-latest, x86_64-unknown-linux-gnu)	1m 4s
Cross-compile (ubuntu-latest, x86_64-pc-windows-gnu)	1m 14s
Cross-compile (ubuntu-latest, wasm32-unknown-unknown)	1m 7s
Cross-compile (macos-latest, x86_64-apple-darwin)	46s
Cross-compile (windows-latest, x86_64-pc-windows-msvc)	1m 42s
	6m 4s

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