k12: new implementation with parallel processing support #46

Job	Run time
minimal-versions / minimal-versions	29s
set-msrv / set-msrv	6s
build (1.85.0, thumbv7em-none-eabi)	19s
build (1.85.0, wasm32-unknown-unknown)	22s
build (stable, wasm32-unknown-unknown)	24s
build (stable, thumbv7em-none-eabi)	19s
test (1.85.0)	56s
test (stable)	53s
	3m 48s

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