Print hex in Debug for Sequence

Printing the `Sequence` as a decimal is not super useful when debugging,
print it in hex instead.

Using code:

        let seq = Sequence::from_consensus(0xFFFFFFFF);
        println!("sequence: {:?}", seq);

Before applying this patch we get:

        sequence: Sequence(4294967295)

And after applying we get:

        sequence: Sequence(0xffffffff)

bitcoin/src/blockdata/transaction.rs

@@ -315,7 +315,7 @@ impl Default for TxIn {
 /// [BIP-65]: <https://github.com/bitcoin/bips/blob/master/bip-0065.mediawiki>
 /// [BIP-68]: <https://github.com/bitcoin/bips/blob/master/bip-0068.mediawiki>
 /// [BIP-125]: <https://github.com/bitcoin/bips/blob/master/bip-0125.mediawiki>
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[cfg_attr(feature = "serde", serde(crate = "actual_serde"))]
 pub struct Sequence(pub u32);
@@ -504,6 +504,13 @@ impl fmt::UpperHex for Sequence {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::UpperHex::fmt(&self.0, f) }
 }
 
+impl fmt::Debug for Sequence {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // 10 because its 8 digits + 2 for the '0x'
+        write!(f, "Sequence({:#010x})", self.0)
+    }
+}
+
 impl_parse_str_from_int_infallible!(Sequence, u32, from_consensus);
 
 /// Bitcoin transaction output.
@@ -2408,6 +2415,12 @@ mod tests {
             InputWeightPrediction::P2PKH_COMPRESSED_MAX.weight()
         );
     }
+
+    #[test]
+    fn sequence_debug_output() {
+        let seq = Sequence::from_seconds_floor(1000);
+        println!("{:?}", seq)
+    }
 }
 
 #[cfg(bench)]