[examples] Remove prost

[BrendanChou]

Fixes #707

[patrick-ogrady]

I suggest building verify() into the type we are verifying itself. See #735 for examples of how to do this.

[BrendanChou]

While it might be nice, I think it doesn't make things that much cleaner in this case. Since each of the enum types are quite different, it doesn't make sense to have a verify() function on the top-level enum (because some types like Abort don't need any information to validate), meaning that there would just be optional verify() functions on the individual structs.

Here's what that would look like, which is actually pretty decent, just kind of weird that you have to re-pass-in the round variable even though it is on the Commitment itself

impl<C: Verifier> Commitment<C> {
    /// Verifies the acknowledgments against the dealer's public commitment.
    pub fn verify(
        &self,
        round: u64,
        dealer: C::PublicKey,
        participants: &Vec<C::PublicKey>,
    ) -> bool {
        let payload = payload(round, &dealer, &self.commitment);
        for (i, signature) in self.acks.iter() {
            let Some(public_key) = participants.get(*i as usize) else {
                return false;
            };
            if !C::verify(Some(ACK_NAMESPACE), &payload, public_key, signature) {
                return false;
            }
        }
        true
    }
}

In this case, most of the actual validation work for Commitment occurs in cryptography/src/bls12381/dkgs/arbiter.rs, so the validation function isn't actually able to remove that much work unless I start reaching into the cryptography module

Especially since this is an example, I suggest we just leave it for now

[BrendanChou]

I have cleaned up the section of code that would have used this function, making it less useful

[patrick-ogrady]

This should now be unblocked!

[patrick-ogrady]

I wonder if it is worth just creating an Ack object and implementing Codec over it?

[BrendanChou]

It mirrors the function here

Let me create an issue to consider modifying both of these functions at once

[BrendanChou]

#774

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.37%. Comparing base (ea036be) to head (7d6ab4b).
Report is 2 commits behind head on main.

@@           Coverage Diff           @@
##             main     #709   +/-   ##
=======================================
  Coverage   89.37%   89.37%           
=======================================
  Files         165      165           
  Lines       41293    41305   +12     
=======================================
+ Hits        36904    36915   +11     
- Misses       4389     4390    +1     

Files with missing lines	Coverage Δ
codec/src/types/primitives.rs	98.94% <100.00%> (-0.02%)	⬇️
cryptography/src/bls12381/dkg/arbiter.rs	96.49% <100.00%> (-0.03%)	⬇️

... and 2 files with indirect coverage changes

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