k12: add `Kt256`; rename `KangarooTwelve` to `Kt128` (#756) #44

Job	Run time
minimal-versions / minimal-versions	54s
set-msrv / set-msrv	5s
test (stable)	26s
test (1.85.0)	32s
build (stable, wasm32-unknown-unknown)	21s
build (1.85.0, wasm32-unknown-unknown)	26s
build (1.85.0, thumbv7em-none-eabi)	23s
build (stable, thumbv7em-none-eabi)	21s
	3m 28s

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