Release k12 v0.4.0 #357

Job	Run time
set-msrv / set-msrv	6s
minimal-versions / minimal-versions	34s
cross (1.85.0, powerpc-unknown-linux-gnu, default)	41s
build (stable, wasm32-unknown-unknown)	26s
cross (1.85.0, aarch64-unknown-linux-gnu, default)	41s
cross (stable, aarch64-unknown-linux-gnu, default)	44s
build (1.85.0, thumbv7em-none-eabi)	21s
build (1.85.0, wasm32-unknown-unknown)	24s
build (stable, thumbv7em-none-eabi)	22s
test (stable)	30s
test (1.85.0)	28s
cross (stable, powerpc-unknown-linux-gnu, default)	1m 11s
	6m 28s

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