Add `alloc` feature with `Box`/`Vec` conversions (#136) #283

Job	Run time
careful	58s
doc	14s
clippy	19s
miri (x86_64-unknown-linux-gnu)	41s
rustfmt	7s
test (1.85.0)	26s
miri (s390x-unknown-linux-gnu)	54s
test (stable)	22s
build (1.85.0, armv7a-none-eabi)	22s
build (1.85.0, thumbv7em-none-eabi)	22s
build (1.85.0, wasm32-unknown-unknown)	23s
build (stable, armv7a-none-eabi)	23s
build (stable, wasm32-unknown-unknown)	19s
build (stable, thumbv7em-none-eabi)	21s
	6m 11s

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