Split methods to extension traits on public keys

diff --git a/bitcoin/src/crypto/key.rs b/bitcoin/src/crypto/key.rs
index c819d317..671915c1 100644
--- a/bitcoin/src/crypto/key.rs
+++ b/bitcoin/src/crypto/key.rs
@@ -19,7 +19,7 @@ use io::{Read, Write};
 
 use crate::crypto::ecdsa;
 use crate::hex::{self, DecodeFixedLengthBytesError};
-use crate::internal_macros::impl_asref_push_bytes;
+use crate::internal_macros::{define_extension_trait, impl_asref_push_bytes};
 use crate::network::NetworkKind;
 use crate::prelude::{DisplayHex, String, Vec};
 use crate::script::{self, PushBytes, WitnessScriptBuf};
@@ -651,20 +651,6 @@ impl LegacyPublicKey {
         }
     }
 
-    /// Returns the script code used to spend a P2WPKH input.
-    ///
-    /// While the type returned is [`WitnessScriptBuf`], this is **not** a witness script and
-    /// should not be used as one. It is a special template defined in BIP 143 which is used
-    /// in place of a witness script for purposes of sighash computation.
-    ///
-    /// # Errors
-    ///
-    /// Errors if this key is not compressed.
-    pub fn p2wpkh_script_code(&self) -> Result<WitnessScriptBuf, UncompressedPublicKeyError> {
-        let key = FullPublicKey::try_from(*self)?;
-        Ok(key.p2wpkh_script_code())
-    }
-
     /// Converts this [`LegacyPublicKey`] into a [`FullPublicKey`] infallibly.
     ///
     /// Unlike the `TryFrom` implementation, this function will discard compressedness
@@ -709,15 +695,6 @@ impl LegacyPublicKey {
         })
     }
 
-    /// Serializes the public key to bytes.
-    pub fn to_bytes(self) -> SerializedLegacyPublicKey {
-        if self.compressed() {
-            SerializedLegacyPublicKey::new_compressed(&self.serialize_compressed())
-        } else {
-            SerializedLegacyPublicKey::new_uncompressed(&self.serialize_uncompressed())
-        }
-    }
-
     /// Serializes the public key to bytes.
     #[allow(clippy::missing_panics_doc)]
     pub fn to_vec(self) -> Vec<u8> {
@@ -833,6 +810,34 @@ impl LegacyPublicKey {
     }
 }
 
+define_extension_trait! {
+    /// Extension functionality for the [`LegacyPublicKey`] type.
+    pub trait LegacyPublicKeyExt impl for LegacyPublicKey {
+        /// Returns the script code used to spend a P2WPKH input.
+        ///
+        /// While the type returned is [`WitnessScriptBuf`], this is **not** a witness script and
+        /// should not be used as one. It is a special template defined in BIP 143 which is used
+        /// in place of a witness script for purposes of sighash computation.
+        ///
+        /// # Errors
+        ///
+        /// Errors if this key is not compressed.
+        fn p2wpkh_script_code(&self) -> Result<WitnessScriptBuf, UncompressedPublicKeyError> {
+            let key = FullPublicKey::try_from(*self)?;
+            Ok(key.p2wpkh_script_code())
+        }
+
+        /// Serializes the public key to bytes.
+        fn to_bytes(self) -> SerializedLegacyPublicKey {
+            if self.compressed() {
+                SerializedLegacyPublicKey::new_compressed(&self.serialize_compressed())
+            } else {
+                SerializedLegacyPublicKey::new_uncompressed(&self.serialize_uncompressed())
+            }
+        }
+    }
+}
+
 impl From<secp256k1::PublicKey> for LegacyPublicKey {
     fn from(pk: secp256k1::PublicKey) -> Self { Self::from_secp(pk) }
 }
@@ -915,15 +920,6 @@ impl FullPublicKey {
         WPubkeyHash::from_byte_array(hash160::Hash::hash(&self.to_bytes()).to_byte_array())
     }
 
-    /// Returns the script code used to spend a P2WPKH input.
-    ///
-    /// While the type returned is [`WitnessScriptBuf`], this is **not** a witness script and
-    /// should not be used as one. It is a special template defined in BIP 143 which is used
-    /// in place of a witness script for purposes of sighash computation.
-    pub fn p2wpkh_script_code(&self) -> WitnessScriptBuf {
-        script::p2wpkh_script_code(self.wpubkey_hash())
-    }
-
     /// Writes the public key into a writer.
     ///
     /// # Errors
@@ -1015,6 +1011,20 @@ impl FullPublicKey {
     }
 }
 
+define_extension_trait! {
+    /// Extension functionality for the [`FullPublicKey`] type.
+    pub trait FullPublicKeyExt impl for FullPublicKey {
+        /// Returns the script code used to spend a P2WPKH input.
+        ///
+        /// While the type returned is [`WitnessScriptBuf`], this is **not** a witness script and
+        /// should not be used as one. It is a special template defined in BIP 143 which is used
+        /// in place of a witness script for purposes of sighash computation.
+        fn p2wpkh_script_code(&self) -> WitnessScriptBuf {
+            script::p2wpkh_script_code(self.wpubkey_hash())
+        }
+    }
+}
+
 impl fmt::Display for FullPublicKey {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         fmt::Display::fmt(&self.to_bytes().as_hex(), f)
@@ -1075,6 +1085,12 @@ impl From<&FullPublicKey> for WPubkeyHash {
     fn from(key: &FullPublicKey) -> Self { key.wpubkey_hash() }
 }
 
+mod sealed {
+    pub trait Sealed {}
+    impl Sealed for super::FullPublicKey {}
+    impl Sealed for super::LegacyPublicKey {}
+}
+
 impl PrivateKey {
     /// Constructs a new compressed ECDSA private key using the secp256k1 algorithm and
     /// a secure random number generator.
diff --git a/bitcoin/src/lib.rs b/bitcoin/src/lib.rs
index 89af016e..83afa6c6 100644
--- a/bitcoin/src/lib.rs
+++ b/bitcoin/src/lib.rs
@@ -101,6 +101,7 @@ pub mod ext {
     #[rustfmt::skip] // Use terse custom grouping.
     pub use crate::{
         block::{BlockCheckedExt as _, HeaderExt as _},
+        key::{FullPublicKeyExt as _, LegacyPublicKeyExt as _},
         pow::CompactTargetExt as _,
         script::{ScriptExt as _, ScriptBufExt as _, TapScriptExt as _, ScriptPubKeyExt as _, ScriptPubKeyBufExt as _, WitnessScriptExt as _, ScriptSigExt as _},
         transaction::{TxidExt as _, WtxidExt as _, OutPointExt as _, TxInExt as _, TxOutExt as _, TransactionExt as _},