feat: Publish protobuf schemas

[michaelhly]

What is the feature you would like to implement?
Publish .proto schemas in @farcaster/protobufs.

Why is this feature important?
Make life easier for automated binding generation, especially in CI environments.

Will the protocol spec need to be updated??
n/a

How should this feature be built? (optional)
Include all the .proto schemas when publishing the @farcaster/protobufs package.

Additional context
Right now this is all the package publishes:

% ls node_modules/@farcaster/protobufs/dist 
index.d.ts	index.js	index.mjs