[EPIC] Horcrux Support

[jackzampolin]

Horcrux should support Gordian!

• Gordian Signer Interface
• Horcrux Signer Interface

THEY ARE THE SAME! This should be very straightforward

I'm pretty sure @agouin already knows whats involved here but also tagging @Reecepbcups and @mark-rushakoff as this implementation bears on the tooling for grpc services. Also Andy for visibiliy.

[jackzampolin]

Note: horcrux uses buf and might be a good opportunity

[Reecepbcups]

ref buf attempt here: https://github.com/rollchains/gordian/tree/reece/grpc-buf-attempt

cosmos gogoproto is not happy with duplicate registrations. When you hack around that, it does not seem to expose the service? despite it being registered and working perfectly with protoc. Maybe a me thing but feels weird

Got it to be happy, but breaks gRPCurl. So technically work can get started on this once we get the base gRPC in and add on top

[mark-rushakoff]

Since we've been discussing it in the background for a while, https://github.com/rollchains/gordian/blob/830ecf50f017e9e6b38788a1b959db80ae870b4e/tm/tmconsensus/signer.go is the new, more tm-aware signer interface -- I believe this API has more context necessary for Horcrux to ensure that members are not double-signing for the same height and round, or something like that. @agouin should know better than I do about this part.