prost 0.7 uses core types instead of std

[greg-szabo]

Prost 0.7 moved all internally used types (Vec, String, etc) generated from the core library, instead of std.

This is cool for our no-std approach but will it have any impact on downstream projects?

What's the definition of "done" for this issue?
Get an answer if we're ok going ahead with using core types in tendermint-proto.
We should rebuild the proto library if this is ok.

[tony-iqlusion]

std is just a facade for core/alloc anyway. It's not really an issue.

[thanethomson]

#862 rebuilds the tendermint-proto crate referencing core instead: https://github.com/informalsystems/tendermint-rs/pull/862/files#diff-5490ef56810f271524d11c1ae79f36be9ec2db0daca7d9f2227dc430efb917b7