Add Clone to `KemCore` and `KemCore::EncapsulationKey` (#79) #82

Job	Run time
minimal-versions	0s
set-msrv / set-msrv	9s
cross (powerpc-unknown-linux-gnu, 1.81.0)	50s
no_std (1.81.0, thumbv7em-none-eabi)	21s
test (1.81.0)	37s
cross (powerpc-unknown-linux-gnu, stable)	50s
no_std (1.81.0, wasm32-unknown-unknown)	19s
test (stable)	36s
no_std (stable, thumbv7em-none-eabi)	24s
no_std (stable, wasm32-unknown-unknown)	23s
	4m 29s

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