add reasons to slash evidence (#414)

* add reasons to slash evidence

* fix CI failing

* Remove unnecessary clones

.encode() takes &self

* InvalidVr to InvalidValidRound

* Unrelated to this PR: Clarify reasoning/potentials behind dropping evidence

* Clarify prevotes in SlashEvidence test

* Replace use of read_to_end

* Restore decode_signed_message

---------

Co-authored-by: Luke Parker <lukeparker5132@gmail.com>

coordinator/tributary/src/lib.rs

@@ -15,6 +15,8 @@ use ::tendermint::{
   TendermintMachine, TendermintHandle,
 };
 
+pub use ::tendermint::Evidence;
+
 use serai_db::Db;
 
 use tokio::sync::RwLock;