feat+refactor: Bump MSRV to `1.83.0` and maximize `const` #229

Job	Run time
nostd/thumbv6m-none-eabi/stable	12s
miri	45s
tests (1.51.0, serde, false, --skip spare_capacity_mut)	29s
tests (1.70.0, serde, false)	13s
tests (stable, true, false)	21s
tests (beta, serde, false)	24s
tests (nightly, serde, borsh, zeroize, false)	23s
	2m 47s

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