kem

Add compatibility section to the `SerializableState` docs (#1694) #1265

Job	Run time
build (1.66.0, thumbv7em-none-eabi)	1m 3s
build (1.66.0, wasm32-unknown-unknown)	1m 4s
test (1.66.0)	1m 31s
build (stable, thumbv7em-none-eabi)	13s
test (stable)	38s
build (stable, wasm32-unknown-unknown)	22s
	4m 51s

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