k12: new implementation with parallel processing support (#839) #1575

Job	Run time
minimal-versions / minimal-versions	50s
set-msrv / set-msrv	4s
test (stable)	54s
cross (stable, aarch64-unknown-linux-gnu, default)	42s
build (stable, thumbv7em-none-eabi)	24s
test (1.85.0)	55s
cross (stable, powerpc-unknown-linux-gnu, default)	44s
cross (1.85.0, powerpc-unknown-linux-gnu, default)	44s
build (1.85.0, thumbv7em-none-eabi)	26s
build (1.85.0, wasm32-unknown-unknown)	28s
build (stable, wasm32-unknown-unknown)	31s
cross (1.85.0, aarch64-unknown-linux-gnu, default)	45s
	7m 27s

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