Panic in evidence serializers

[romac]

The serializers for tendermint::types::{Evidence, evidence::Sum} are incomplete and may cause a panic in the relayer.

The panic happens in this From instance, which should likely be converted to a TryFrom instance:

tendermint-rs/proto/src/serializers/evidence.rs

Lines 30 to 38 in 4cbf727

	impl From<Evidence> for EvidenceVariant {
	fn from(value: Evidence) -> Self {
	let sum = value.sum.unwrap(); // Todo: Error handling
	match sum {
	Sum::DuplicateVoteEvidence(d) => Self::DuplicateVoteEvidence(d),
	Sum::LightClientAttackEvidence(l) => Self::LightClientAttackEvidence(l),
	}
	}
	}

Additionally, these From instances are currently unimplemented!:

tendermint-rs/proto/src/serializers/evidence.rs

Lines 40 to 50 in 4cbf727

	impl From<Sum> for EvidenceVariant {
	fn from(_: Sum) -> Self {
	unimplemented!() // Prost adds extra annotations on top of Sum that are not used.
	}
	}
	impl From<EvidenceVariant> for Sum {
	fn from(_: EvidenceVariant) -> Self {
	unimplemented!() // Prost adds extra annotations on top of Sum that are not used.
	}
	}

The comment seems to imply they won't ever be called, so it shouldn't be a problem, but perhaps it would worth looking into removing them altogether while we're at it.