primitives: Re-order encoding code

diff --git a/primitives/src/block.rs b/primitives/src/block.rs
index d800e9c9..16755e92 100644
--- a/primitives/src/block.rs
+++ b/primitives/src/block.rs
@@ -324,15 +324,6 @@ impl<V: Validation> fmt::UpperHex for Block<V> {
     }
 }
 
-#[cfg(feature = "alloc")]
-encoding::encoder_newtype! {
-    /// The encoder for the [`Block`] type.
-    #[derive(Debug, Clone)]
-    pub struct BlockEncoder<'e>(
-        Encoder2<HeaderEncoder<'e>, Encoder2<CompactSizeEncoder, SliceEncoder<'e, Transaction>>>
-    );
-}
-
 #[cfg(feature = "alloc")]
 impl<V> encoding::Encode for Block<V>
 where
@@ -354,6 +345,20 @@ where
     }
 }
 
+#[cfg(feature = "alloc")]
+impl encoding::Decode for Block<Unchecked> {
+    type Decoder = BlockDecoder;
+}
+
+#[cfg(feature = "alloc")]
+encoding::encoder_newtype! {
+    /// The encoder for the [`Block`] type.
+    #[derive(Debug, Clone)]
+    pub struct BlockEncoder<'e>(
+        Encoder2<HeaderEncoder<'e>, Encoder2<CompactSizeEncoder, SliceEncoder<'e, Transaction>>>
+    );
+}
+
 #[cfg(feature = "alloc")]
 type BlockInnerDecoder = Decoder2<HeaderDecoder, VecDecoder<Transaction>>;
 
@@ -374,11 +379,6 @@ crate::decoder_newtype! {
     }
 }
 
-#[cfg(feature = "alloc")]
-impl encoding::Decode for Block<Unchecked> {
-    type Decoder = BlockDecoder;
-}
-
 /// Computes the Merkle root for a list of transactions.
 ///
 /// Returns `None` if the iterator was empty, or if the transaction list contains
@@ -523,21 +523,6 @@ impl fmt::Debug for Header {
     }
 }
 
-encoding::encoder_newtype_exact! {
-    /// The encoder for the [`Header`] type.
-    #[derive(Debug, Clone)]
-    pub struct HeaderEncoder<'e>(
-        encoding::Encoder6<
-            VersionEncoder<'e>,
-            BlockHashEncoder<'e>,
-            crate::merkle_tree::TxMerkleNodeEncoder<'e>,
-            crate::time::BlockTimeEncoder<'e>,
-            crate::pow::CompactTargetEncoder<'e>,
-            encoding::ArrayEncoder<4>,
-        >
-    );
-}
-
 impl encoding::Encode for Header {
     type Encoder<'e> = HeaderEncoder<'e>;
 
@@ -553,6 +538,25 @@ impl encoding::Encode for Header {
     }
 }
 
+impl encoding::Decode for Header {
+    type Decoder = HeaderDecoder;
+}
+
+encoding::encoder_newtype_exact! {
+    /// The encoder for the [`Header`] type.
+    #[derive(Debug, Clone)]
+    pub struct HeaderEncoder<'e>(
+        encoding::Encoder6<
+            VersionEncoder<'e>,
+            BlockHashEncoder<'e>,
+            crate::merkle_tree::TxMerkleNodeEncoder<'e>,
+            crate::time::BlockTimeEncoder<'e>,
+            crate::pow::CompactTargetEncoder<'e>,
+            encoding::ArrayEncoder<4>,
+        >
+    );
+}
+
 type HeaderInnerDecoder = Decoder6<
     VersionDecoder,
     BlockHashDecoder,
@@ -605,10 +609,6 @@ impl HeaderDecoder {
     }
 }
 
-impl encoding::Decode for Header {
-    type Decoder = HeaderDecoder;
-}
-
 impl From<Header> for BlockHash {
     #[inline]
     fn from(header: Header) -> Self { header.block_hash() }
@@ -716,12 +716,6 @@ impl Default for Version {
     fn default() -> Self { Self::NO_SOFT_FORK_SIGNALLING }
 }
 
-encoding::encoder_newtype_exact! {
-    /// The encoder for the [`Version`] type.
-    #[derive(Debug, Clone)]
-    pub struct VersionEncoder<'e>(encoding::ArrayEncoder<4>);
-}
-
 impl encoding::Encode for Version {
     type Encoder<'e> = VersionEncoder<'e>;
     fn encoder(&self) -> Self::Encoder<'_> {
@@ -731,6 +725,16 @@ impl encoding::Encode for Version {
     }
 }
 
+impl encoding::Decode for Version {
+    type Decoder = VersionDecoder;
+}
+
+encoding::encoder_newtype_exact! {
+    /// The encoder for the [`Version`] type.
+    #[derive(Debug, Clone)]
+    pub struct VersionEncoder<'e>(encoding::ArrayEncoder<4>);
+}
+
 crate::decoder_newtype! {
     /// The decoder for the [`Version`] type.
     #[derive(Debug, Clone)]
@@ -746,10 +750,6 @@ crate::decoder_newtype! {
     }
 }
 
-impl encoding::Decode for Version {
-    type Decoder = VersionDecoder;
-}
-
 /// Error types for Bitcoin blocks.
 pub mod error {
     use core::convert::Infallible;
diff --git a/primitives/src/script/borrowed.rs b/primitives/src/script/borrowed.rs
index 0b1a7cad..66e6630b 100644
--- a/primitives/src/script/borrowed.rs
+++ b/primitives/src/script/borrowed.rs
@@ -183,12 +183,6 @@ impl<T> Script<T> {
     pub fn to_hex(&self) -> alloc::string::String { alloc::format!("{:x}", self) }
 }
 
-encoding::encoder_newtype_exact! {
-    /// The encoder for the [`Script<T>`] type.
-    #[derive(Debug, Clone)]
-    pub struct ScriptEncoder<'e>(Encoder2<CompactSizeEncoder, BytesEncoder<'e>>);
-}
-
 impl<T> Encode for Script<T> {
     type Encoder<'e>
         = ScriptEncoder<'e>
@@ -203,6 +197,12 @@ impl<T> Encode for Script<T> {
     }
 }
 
+encoding::encoder_newtype_exact! {
+    /// The encoder for the [`Script<T>`] type.
+    #[derive(Debug, Clone)]
+    pub struct ScriptEncoder<'e>(Encoder2<CompactSizeEncoder, BytesEncoder<'e>>);
+}
+
 #[cfg(feature = "arbitrary")]
 impl<'a, T> Arbitrary<'a> for &'a Script<T> {
     #[inline]
diff --git a/primitives/src/script/owned.rs b/primitives/src/script/owned.rs
index a9fc9c8f..31a38226 100644
--- a/primitives/src/script/owned.rs
+++ b/primitives/src/script/owned.rs
@@ -180,6 +180,10 @@ impl<T> DerefMut for ScriptBuf<T> {
     fn deref_mut(&mut self) -> &mut Self::Target { self.as_mut_script() }
 }
 
+impl<T> encoding::Decode for ScriptBuf<T> {
+    type Decoder = ScriptBufDecoder<T>;
+}
+
 /// The decoder for the [`ScriptBuf`] type.
 #[derive(Debug, Clone)]
 pub struct ScriptBufDecoder<T>(ByteVecDecoder, PhantomData<T>);
@@ -211,10 +215,6 @@ impl<T> encoding::Decoder for ScriptBufDecoder<T> {
     fn read_limit(&self) -> usize { self.0.read_limit() }
 }
 
-impl<T> encoding::Decode for ScriptBuf<T> {
-    type Decoder = ScriptBufDecoder<T>;
-}
-
 #[cfg(feature = "arbitrary")]
 impl<'a, T> Arbitrary<'a> for ScriptBuf<T> {
     #[inline]
diff --git a/primitives/src/witness.rs b/primitives/src/witness.rs
index 2362eb48..618debc8 100644
--- a/primitives/src/witness.rs
+++ b/primitives/src/witness.rs
@@ -280,10 +280,6 @@ fn decode_cursor(bytes: &[u8], start_of_indices: usize, index: usize) -> Option<
     usize::try_from(pos).ok()
 }
 
-/// The encoder for the [`Witness`] type.
-#[derive(Debug, Clone)]
-pub struct WitnessEncoder<'e>(Encoder2<CompactSizeEncoder, BytesEncoder<'e>>);
-
 impl encoding::Encode for Witness {
     type Encoder<'e>
         = WitnessEncoder<'e>
@@ -299,6 +295,14 @@ impl encoding::Encode for Witness {
     }
 }
 
+impl encoding::Decode for Witness {
+    type Decoder = WitnessDecoder;
+}
+
+/// The encoder for the [`Witness`] type.
+#[derive(Debug, Clone)]
+pub struct WitnessEncoder<'e>(Encoder2<CompactSizeEncoder, BytesEncoder<'e>>);
+
 impl encoding::Encoder for WitnessEncoder<'_> {
     #[inline]
     fn current_chunk(&self) -> &[u8] { self.0.current_chunk() }
@@ -531,10 +535,6 @@ impl encoding::Decoder for WitnessDecoder {
     }
 }
 
-impl encoding::Decode for Witness {
-    type Decoder = WitnessDecoder;
-}
-
 // Note: we use `Borrow` in the following `PartialEq` impls specifically because of its additional
 // constraints on equality semantics.
 impl<T: core::borrow::Borrow<[u8]>> PartialEq<[T]> for Witness {