Introduce TxInExt trait

In preparation for moving the `TxIn` over to `primitives` introduce an
extension trait.

bitcoin/src/blockdata/transaction.rs

@@ -129,7 +129,9 @@ impl TxIn {
     };
 }
 
-impl TxIn {
+crate::internal_macros::define_extension_trait! {
+    /// Extension functionality for the [`TxIn`] type.
+    pub trait TxInExt impl for TxIn {
         /// Returns true if this input enables the [`absolute::LockTime`] (aka `nLockTime`) of its
         /// [`Transaction`].
         ///
@@ -139,7 +141,7 @@ impl TxIn {
         ///  this input then the script execution will fail [BIP-0065].
         ///
         /// [BIP-65](https://github.com/bitcoin/bips/blob/master/bip-0065.mediawiki)
-    pub fn enables_lock_time(&self) -> bool { self.sequence != Sequence::MAX }
+        fn enables_lock_time(&self) -> bool { self.sequence != Sequence::MAX }
 
         /// The weight of the TxIn when it's included in a legacy transaction (i.e., a transaction
         /// having only legacy inputs).
@@ -150,7 +152,7 @@ impl TxIn {
         /// Keep in mind that when adding a TxIn to a transaction, the total weight of the transaction
         /// might increase more than `TxIn::legacy_weight`. This happens when the new input added causes
         /// the input length `VarInt` to increase its encoding length.
-    pub fn legacy_weight(&self) -> Weight {
+        fn legacy_weight(&self) -> Weight {
             Weight::from_non_witness_data_size(self.base_size().to_u64())
         }
 
@@ -165,7 +167,7 @@ impl TxIn {
         /// - the new input added causes the input length `VarInt` to increase its encoding length
         /// - the new input is the first segwit input added - this will add an additional 2WU to the
         ///   transaction weight to take into account the segwit marker
-    pub fn segwit_weight(&self) -> Weight {
+        fn segwit_weight(&self) -> Weight {
             Weight::from_non_witness_data_size(self.base_size().to_u64())
                 + Weight::from_witness_data_size(self.witness.size().to_u64())
         }
@@ -173,7 +175,7 @@ impl TxIn {
         /// Returns the base size of this input.
         ///
         /// Base size excludes the witness data (see [`Self::total_size`]).
-    pub fn base_size(&self) -> usize {
+        fn base_size(&self) -> usize {
             let mut size = OutPoint::SIZE;
 
             size += compact_size::encoded_size(self.script_sig.len());
@@ -185,7 +187,8 @@ impl TxIn {
         /// Returns the total number of bytes that this input contributes to a transaction.
         ///
         /// Total size includes the witness data (for base size see [`Self::base_size`]).
-    pub fn total_size(&self) -> usize { self.base_size() + self.witness.size() }
+        fn total_size(&self) -> usize { self.base_size() + self.witness.size() }
+    }
 }
 
 /// Bitcoin transaction output.
@@ -1338,6 +1341,7 @@ mod sealed {
     impl Sealed for super::Txid {}
     impl Sealed for super::Wtxid {}
     impl Sealed for super::OutPoint {}
+    impl Sealed for super::TxIn {}
     impl Sealed for super::TxOut {}
     impl Sealed for super::Version {}
 }