Use `Box<[u8]>` instead of `Vec<u8>` in `Serialized` #621

Job	Run time
set-env	2s
build-binaries-x64	2m 37s
build-binaries-ext (powerpc64le-unknown-linux-gnu, powerpc64)	2m 26s
build-python-binding	6m 12s
build-binaries-ext (armv7-unknown-linux-gnueabihf, raspberry-pi)	2m 23s
build-binaries-ext (aarch64-unknown-linux-gnu, arm64-linux)	2m 47s
	16m 27s

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