feat: Add TokenTransfer class to Curve

- This needed to be in Curve so that the executor can also take care of transfers from the user into the tycho router, to avoid having transfer actions mixed between the router and executors

src/encoding/evm/strategy_encoder/transfer_optimizations.rs

@@ -27,11 +27,11 @@ pub trait TransferOptimization {
         let is_first_swap =
             (swap.token_in == given_token) || ((swap.token_in == wrapped_token) && wrap);
 
-        if is_first_swap && send_funds_to_pool {
-            if swap.token_in == native_token {
-                // Funds are already in router. Protocol takes care of native transfer.
-                TransferType::None
-            } else if permit2 {
+        if swap.token_in == native_token {
+            // Funds are already in router. All protocols currently take care of native transfers.
+            TransferType::None
+        } else if is_first_swap && send_funds_to_pool {
+            if permit2 {
                 // Transfer from swapper to pool using permit2.
                 TransferType::Permit2Transfer
             } else {
@@ -39,10 +39,7 @@ pub trait TransferOptimization {
                 TransferType::TransferFrom
             }
         } else if is_first_swap && funds_expected_in_router {
-            if swap.token_in == native_token {
-                // Funds already in router. Do nothing.
-                TransferType::None
-            } else if permit2 {
+            if permit2 {
                 // Transfer from swapper to router using permit2.
                 TransferType::Permit2TransferToRouter
             } else {