perf: lock the known transmissions when checking the batch header

Signed-off-by: ljedrz <[email protected]>

node/narwhal/src/helpers/storage.rs

@@ -337,10 +337,12 @@ impl<N: Network> Storage<N> {
 
         // Initialize a list for the missing transmissions from storage.
         let mut missing_transmissions = HashMap::new();
+        // Lock the existing transmissions.
+        let known_transmissions = self.transmissions.read();
         // Ensure the declared transmission IDs are all present in storage or the given transmissions map.
         for transmission_id in batch_header.transmission_ids() {
             // If the transmission ID does not exist, ensure it was provided by the caller.
-            if !self.transmissions.read().contains_key(transmission_id) {
+            if !known_transmissions.contains_key(transmission_id) {
                 // Retrieve the transmission.
                 let Some(transmission) = transmissions.remove(transmission_id) else {
                     bail!("Failed to provide a transmission for round {round} {gc_log}");