feat(wasm-utxo): add BitGoPsbt.into_psbt method to convert to standard Psbt

The method allows for extracting a standard Psbt from either Bitcoin-like or
Zcash PSBTs, which simplifies transaction finalization. Tests verify that
extracted transactions match expected hex values.

Issue: BTC-2652

Co-authored-by: llm-git <[email protected]>

Author: OttoAllmendinger

packages/wasm-utxo/src/bitgo_psbt/mod.rs

@@ -133,18 +133,26 @@ impl BitGoPsbt {
             BitGoPsbt::Zcash(zcash_psbt, _network) => Ok(zcash_psbt.serialize()?),
         }
     }
+
+    pub fn into_psbt(self) -> Psbt {
+        match self {
+            BitGoPsbt::BitcoinLike(psbt, _network) => psbt,
+            BitGoPsbt::Zcash(zcash_psbt, _network) => zcash_psbt.into_bitcoin_psbt(),
+        }
+    }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::fixed_script_wallet::Chain;
     use crate::fixed_script_wallet::{RootWalletKeys, WalletScripts};
     use crate::test_utils::fixtures;
-    use crate::fixed_script_wallet::Chain;
     use base64::engine::{general_purpose::STANDARD as BASE64_STANDARD, Engine};
     use miniscript::bitcoin::bip32::Xpub;
     use miniscript::bitcoin::consensus::Decodable;
     use miniscript::bitcoin::Transaction;
+    
     use std::str::FromStr;
 
     crate::test_all_networks!(test_deserialize_invalid_bytes, network, {
@@ -531,6 +539,32 @@ mod tests {
         }
     );
 
+    crate::test_psbt_fixtures!(test_extract_transaction, network, {
+        let fixture = fixtures::load_psbt_fixture_with_format(
+            network.to_utxolib_name(),
+            fixtures::SignatureState::Fullsigned,
+            fixtures::TxFormat::Psbt,
+        )
+        .expect("Failed to load fixture");
+        let psbt = fixture
+            .to_bitgo_psbt(network)
+            .expect("Failed to convert to BitGo PSBT");
+        let fixture_extracted_transaction = fixture
+            .extracted_transaction
+            .expect("Failed to extract transaction");
+        let extracted_transaction = psbt
+            .into_psbt()
+            .finalize(&crate::bitcoin::secp256k1::Secp256k1::verification_only())
+            .expect("Failed to finalize PSBT")
+            .extract_tx()
+            .expect("Failed to extract transaction");
+        let extracted_transaction_hex = hex::encode(serialize(&extracted_transaction));
+        assert_eq!(
+            extracted_transaction_hex, fixture_extracted_transaction,
+            "Extracted transaction should match"
+        );
+    });
+
     #[test]
     fn test_serialize_bitcoin_psbt() {
         // Test that Bitcoin-like PSBTs can be serialized
@@ -539,7 +573,9 @@ mod tests {
             fixtures::SignatureState::Unsigned,
         )
         .unwrap();
-        let psbt = fixture.to_bitgo_psbt(Network::Bitcoin).expect("Failed to convert to BitGo PSBT");
+        let psbt = fixture
+            .to_bitgo_psbt(Network::Bitcoin)
+            .expect("Failed to convert to BitGo PSBT");
 
         // Serialize should succeed
         let serialized = psbt.serialize();