Update Rust nightly

Supersedes #368.

Adds exceptions for unwrap_or_default due to preference against Default's
ambiguity.

coordinator/tributary/src/mempool.rs

@@ -35,6 +35,7 @@ impl<D: Db, T: TransactionTrait> Mempool<D, T> {
     let tx_hash = tx.hash();
     let transaction_key = self.transaction_key(&tx_hash);
     let current_mempool_key = self.current_mempool_key();
+    #[allow(clippy::unwrap_or_default)]
     let mut current_mempool = self.db.get(&current_mempool_key).unwrap_or(vec![]);
 
     let mut txn = self.db.txn();
@@ -225,6 +226,7 @@ impl<D: Db, T: TransactionTrait> Mempool<D, T> {
   pub(crate) fn remove(&mut self, tx: &[u8; 32]) {
     let transaction_key = self.transaction_key(tx);
     let current_mempool_key = self.current_mempool_key();
+    #[allow(clippy::unwrap_or_default)]
     let current_mempool = self.db.get(&current_mempool_key).unwrap_or(vec![]);
 
     let mut i = 0;

coordinator/tributary/src/provided.rs

@@ -77,6 +77,7 @@ impl<D: Db, T: Transaction> ProvidedTransactions<D, T> {
     }
 
     let current_provided_key = self.current_provided_key();
+    #[allow(clippy::unwrap_or_default)]
     let mut currently_provided = self.db.get(&current_provided_key).unwrap_or(vec![]);
 
     let mut txn = self.db.txn();

coordinator/tributary/tendermint/src/message_log.rs

@@ -19,7 +19,10 @@ impl<N: Network> MessageLog<N> {
   // Returns true if it's a new message
   pub(crate) fn log(&mut self, signed: SignedMessageFor<N>) -> Result<bool, TendermintError<N>> {
     let msg = &signed.msg;
+    // Clarity, and safety around default != new edge cases
+    #[allow(clippy::unwrap_or_default)]
     let round = self.log.entry(msg.round).or_insert_with(HashMap::new);
+    #[allow(clippy::unwrap_or_default)]
     let msgs = round.entry(msg.sender).or_insert_with(HashMap::new);
 
     // Handle message replays without issue. It's only multiple messages which is malicious