feat: Bring back TransferType and simplify encoding logic

Took 1 hour 53 minutes

src/encoding/models.rs

@@ -106,9 +106,7 @@ pub struct Transaction {
 ///   solution does not require router address.
 /// * `group_token_in`: Token to be used as the input for the group swap.
 /// * `group_token_out`: Token to be used as the output for the group swap.
-/// * `transfer_from_needed`: true if the solution requires a transfer from the user to the router
-///   or pool.
-/// * `transfer_needed`: true if the solution requires a transfer from the router to the pool.
+/// * `transfer`: Type of transfer to be performed. See `TransferType` for more details.
 #[derive(Clone, Debug)]
 pub struct EncodingContext {
     pub receiver: Bytes,
@@ -116,8 +114,22 @@ pub struct EncodingContext {
     pub router_address: Option<Bytes>,
     pub group_token_in: Bytes,
     pub group_token_out: Bytes,
-    pub transfer_from_needed: bool,
-    pub transfer_needed: bool,
+    pub transfer: TransferType,
+}
+
+/// Represents the type of transfer to be performed into the pool.
+///
+/// # Fields
+///
+/// * `Transfer`: Transfer the token from the router into the protocol.
+/// * `TransferFrom`: Transfer the token from the sender to the protocol/router.
+/// * `None`: No transfer is needed. Tokens are already in the pool.
+#[repr(u8)]
+#[derive(Clone, Debug, PartialEq)]
+pub enum TransferType {
+    TransferFrom = 0,
+    Transfer = 1,
+    None = 2,
 }
 
 #[derive(Clone, PartialEq, Eq, Hash)]