k12: new implementation with parallel processing support #336

Job	Run time
set-msrv / set-msrv	4s
minimal-versions / minimal-versions	30s
test (stable)	2m 25s
test (1.85.0)	26s
cross (1.85.0, aarch64-unknown-linux-gnu, default)	44s
cross (stable, aarch64-unknown-linux-gnu, default)	41s
cross (stable, powerpc-unknown-linux-gnu, default)	2m 25s
cross (1.85.0, powerpc-unknown-linux-gnu, default)	2m 25s
build (1.85.0, thumbv7em-none-eabi)	2m 25s
build (stable, thumbv7em-none-eabi)	2m 25s
build (stable, wasm32-unknown-unknown)	2m 25s
build (1.85.0, wasm32-unknown-unknown)	2m 25s
	19m 20s

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