Bump `serdect` to v0.3.0-rc.0 #444

Job	Run time
build (1.73.0, thumbv7em-none-eabi)	26s
doc	53s
build (1.73.0, wasm32-unknown-unknown)	26s
build (stable, thumbv7em-none-eabi)	22s
build (stable, wasm32-unknown-unknown)	19s
test (i686-unknown-linux-gnu, 1.73.0, sudo apt update && sudo apt install gcc-multilib)	1m 5s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	1m 0s
test (x86_64-unknown-linux-gnu, 1.73.0)	51s
test (x86_64-unknown-linux-gnu, stable)	39s
	6m 1s

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