Add weight, size, and vsize methods on the Transaction type

bdk-ffi/src/bdk.udl

@@ -244,10 +244,16 @@ interface FeeRate {
 };
 
 interface Transaction {
-   [Throws=BdkError]
-   constructor(sequence<u8> transaction_bytes);
+  [Throws=BdkError]
+  constructor(sequence<u8> transaction_bytes);
 
-   sequence<u8> serialize();
+  sequence<u8> serialize();
+
+  u64 weight();
+
+  u64 size();
+
+  u64 vsize();
 };
 
 interface PartiallySignedTransaction {

bdk-ffi/src/lib.rs

@@ -254,6 +254,18 @@ impl Transaction {
     fn serialize(&self) -> Vec<u8> {
         self.internal.serialize()
     }
+
+    fn weight(&self) -> u64 {
+        self.internal.weight() as u64
+    }
+
+    fn size(&self) -> u64 {
+        self.internal.size() as u64
+    }
+
+    fn vsize(&self) -> u64 {
+        self.internal.vsize() as u64
+    }
 }
 
 /// A Bitcoin address.