add conversions from TXIDs to merkle nodes

bitcoin/src/hash_types.rs

@@ -94,4 +94,16 @@ mod newtypes {
 
     impl_hashencode!(FilterHash);
     impl_hashencode!(FilterHeader);
+
+    impl From<Txid> for TxMerkleNode {
+        fn from(txid: Txid) -> Self {
+            Self::from(txid.0)
+        }
+    }
+
+    impl From<Wtxid> for WitnessMerkleNode {
+        fn from(wtxid: Wtxid) -> Self {
+            Self::from(wtxid.0)
+        }
+    }
 }