Release k12 v0.4.0 #904

Job	Run time
set-msrv / set-msrv	5s
minimal-versions / minimal-versions	25s
build (1.85.0, thumbv7em-none-eabi)	24s
build (stable, thumbv7em-none-eabi)	25s
test (stable)	32s
test (1.85.0)	30s
build (stable, wasm32-unknown-unknown)	20s
build (1.85.0, wasm32-unknown-unknown)	23s
	3m 4s

Provide feedback