feat: continue transactions with request builder (#253)

* feat: transactions can be continued in builder

* feat: signing payload can be requested from unsigned transactions

Removes the need to import the prism_serde trait for encoding.

* chore: Incorporate changes in zkvm elf

Author: jns-ps

crates/common/src/builder.rs

@@ -35,6 +35,13 @@ where
     pub fn to_modify_account(self, account: &Account) -> ModifyAccountRequestBuilder<'a, P> {
         ModifyAccountRequestBuilder::new(self.prism, account)
     }
+
+    pub fn continue_transaction(
+        self,
+        unsigned_transaction: UnsignedTransaction,
+    ) -> SigningTransactionRequestBuilder<'a, P> {
+        SigningTransactionRequestBuilder::new(self.prism, unsigned_transaction)
+    }
 }
 
 impl<P> Default for RequestBuilder<'_, P>

crates/common/src/transaction.rs

@@ -23,7 +23,7 @@ pub struct UnsignedTransaction {
 impl UnsignedTransaction {
     /// Signs the transaction with the given [`SigningKey`] and gives out a full [`Transaction`].
     pub fn sign(self, sk: &SigningKey) -> Result<Transaction, TransactionError> {
-        let bytes = self.encode_to_bytes().map_err(|_| TransactionError::EncodingFailed)?;
+        let bytes = self.signing_payload()?;
         let signature = sk.sign(&bytes);
 
         Ok(Transaction {
@@ -47,6 +47,11 @@ impl UnsignedTransaction {
             vk: signature_bundle.verifying_key,
         }
     }
+
+    /// Returns the transaction's payload that needs to be signed, or a TransactionError if encoding fails.
+    pub fn signing_payload(&self) -> Result<Vec<u8>, TransactionError> {
+        self.encode_to_bytes().map_err(|_| TransactionError::EncodingFailed)
+    }
 }
 
 #[derive(Clone, Serialize, Deserialize, Debug, PartialEq, ToSchema)]