Use expect for concensus_encode on Vec

Calls to `unwrap` outside of tests are typically unfavourable.

In memory writers (`Vec`) do not error. We can use `expect` with a
descriptive message string to indicate this.

src/consensus/encode.rs

@@ -138,7 +138,7 @@ impl From<psbt::Error> for Error {
 /// Encode an object into a vector
 pub fn serialize<T: Encodable + ?Sized>(data: &T) -> Vec<u8> {
     let mut encoder = Vec::new();
-    let len = data.consensus_encode(&mut encoder).unwrap();
+    let len = data.consensus_encode(&mut encoder).expect("in-memory writers don't error");
     debug_assert_eq!(len, encoder.len());
     encoder
 }

src/util/bip158.rs

@@ -365,7 +365,7 @@ impl<'a> GCSFilterWriter<'a> {
 
         // write number of elements as varint
         let mut encoder = Vec::new();
-        VarInt(mapped.len() as u64).consensus_encode(&mut encoder).unwrap();
+        VarInt(mapped.len() as u64).consensus_encode(&mut encoder).expect("in-memory writers don't error");
         let mut wrote = self.writer.write(encoder.as_slice())?;
 
         // write out deltas of sorted values into a Golonb-Rice coded bit stream

src/util/hash.rs

@@ -45,8 +45,8 @@ pub fn bitcoin_merkle_root_inline<T>(data: &mut [T]) -> T
         let idx1 = 2 * idx;
         let idx2 = min(idx1 + 1, data.len() - 1);
         let mut encoder = T::engine();
-        data[idx1].consensus_encode(&mut encoder).unwrap();
-        data[idx2].consensus_encode(&mut encoder).unwrap();
+        data[idx1].consensus_encode(&mut encoder).expect("in-memory writers don't error");
+        data[idx2].consensus_encode(&mut encoder).expect("in-memory writers don't error");
         data[idx] = T::from_engine(encoder);
     }
     let half_len = data.len() / 2 + data.len() % 2;
@@ -73,8 +73,8 @@ pub fn bitcoin_merkle_root<T, I>(mut iter: I) -> T
         // If the size is odd, use the last element twice.
         let hash2 = iter.next().unwrap_or(hash1);
         let mut encoder = T::engine();
-        hash1.consensus_encode(&mut encoder).unwrap();
-        hash2.consensus_encode(&mut encoder).unwrap();
+        hash1.consensus_encode(&mut encoder).expect("in-memory writers don't error");
+        hash2.consensus_encode(&mut encoder).expect("in-memory writers don't error");
         alloc.push(T::from_engine(encoder));
     }
     bitcoin_merkle_root_inline(&mut alloc)