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/user_approvals_manager.rs

@@ -11,5 +11,5 @@ pub struct Approval {
 
 pub trait UserApprovalsManager {
     #[allow(dead_code)]
-    fn encode_approvals(&self, approvals: Vec<Approval>) -> Vec<u8>;
+    fn encode_approvals(&self, approvals: Vec<Approval>) -> Vec<Vec<u8>>;
 }