k12

k12: add `Kt256`; rename `KangarooTwelve` to `Kt128` (#756) #1379

Job	Run time
set-msrv / set-msrv	4s
test (stable)	26s
test (1.85.0)	25s
build (stable, wasm32-unknown-unknown)	23s
build (1.85.0, wasm32-unknown-unknown)	26s
build (stable, thumbv7em-none-eabi)	22s
build (1.85.0, thumbv7em-none-eabi)	20s
	2m 26s

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