feat: Simplify StrategyEncoders and RouterEncoder

No more SingleSwapStrategyEncoder or SequentialStrategyEncoder
No more batch routing (so no need for batch permits as well). If multiple solutions are found, return multiple Transactions

--- don't change below this line ---
ENG-4076 <#DTT#>

src/encoding/router_encoder.rs

@@ -8,6 +8,6 @@ use crate::encoding::{
 
 #[allow(dead_code)]
 pub trait RouterEncoder<S: StrategySelector, A: UserApprovalsManager> {
-    fn encode_router_calldata(&self, solutions: Vec<Solution>) -> Result<Transaction, Error>;
-    fn handle_approvals(&self, solutions: &[Solution]) -> Result<Vec<u8>, Error>;
+    fn encode_router_calldata(&self, solutions: Vec<Solution>) -> Result<Vec<Transaction>, Error>;
+    fn handle_approvals(&self, solutions: &[Solution]) -> Result<Vec<Vec<u8>>, Error>;
 }