Bring back legacy proto #9

Job	Run time
Check rustdoc intra-doc links	42s
Test Suite	2m 1s
Clippy	51s
Check	1m 36s
Cross compile (armv7-unknown-linux-gnueabihf)	13s
Cross compile (powerpc64-unknown-linux-gnu)	33s
Rustfmt	23s
Cross compile (powerpc-unknown-linux-gnu)	18s
Cross compile (wasm32-unknown-unknown)	21s
	6m 58s

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