optimise TransactionFetcher (#6012)

Co-authored-by: zerosnacks <95942363+zerosnacks@users.noreply.github.com>

crates/net/eth-wire/src/types/broadcast.rs

@@ -144,6 +144,14 @@ impl NewPooledTransactionHashes {
         }
     }
 
+    /// Returns a mutable reference to transaction hashes.
+    pub fn hashes_mut(&mut self) -> &mut Vec<B256> {
+        match self {
+            NewPooledTransactionHashes::Eth66(msg) => &mut msg.0,
+            NewPooledTransactionHashes::Eth68(msg) => &mut msg.hashes,
+        }
+    }
+
     /// Consumes the type and returns all hashes
     pub fn into_hashes(self) -> Vec<B256> {
         match self {
@@ -188,6 +196,15 @@ impl NewPooledTransactionHashes {
             NewPooledTransactionHashes::Eth68(msg) => msg.hashes.len(),
         }
     }
+
+    /// Returns an iterator over tx hashes zipped with corresponding eth68 metadata if this is
+    /// an eth68 message.
+    pub fn as_eth68(&self) -> Option<&NewPooledTransactionHashes68> {
+        match self {
+            NewPooledTransactionHashes::Eth66(_) => None,
+            NewPooledTransactionHashes::Eth68(msg) => Some(msg),
+        }
+    }
 }
 
 impl From<NewPooledTransactionHashes> for EthMessage {
@@ -265,6 +282,13 @@ pub struct NewPooledTransactionHashes68 {
     pub hashes: Vec<B256>,
 }
 
+impl NewPooledTransactionHashes68 {
+    /// Returns an iterator over tx hashes zipped with corresponding metadata.
+    pub fn metadata_iter(&self) -> impl Iterator<Item = (&B256, (u8, usize))> {
+        self.hashes.iter().zip(self.types.iter().copied().zip(self.sizes.iter().copied()))
+    }
+}
+
 impl Encodable for NewPooledTransactionHashes68 {
     fn encode(&self, out: &mut dyn bytes::BufMut) {
         #[derive(RlpEncodable)]