fix(optimism): Prevent repeated executions of current flashblock sequence (#18224)

Author: RomanHodulak

crates/optimism/flashblocks/src/service.rs

@@ -37,6 +37,7 @@ pub struct FlashBlockService<
     rx: S,
     current: Option<PendingBlock<N>>,
     blocks: FlashBlockSequence<N::SignedTx>,
+    rebuild: bool,
     evm_config: EvmConfig,
     provider: Provider,
     canon_receiver: CanonStateNotifications<N>,
@@ -71,6 +72,7 @@ where
             canon_receiver: provider.subscribe_to_canonical_state(),
             provider,
             cached_state: None,
+            rebuild: false,
         }
     }
 
@@ -187,17 +189,13 @@ where
     fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
         let this = self.get_mut();
 
-        let mut new_flashblock = false;
         // consume new flashblocks while they're ready
         while let Poll::Ready(Some(result)) = this.rx.poll_next_unpin(cx) {
             match result {
-                Ok(flashblock) => {
-                    if let Err(err) = this.blocks.insert(flashblock) {
-                        debug!(%err, "Failed to prepare flashblock");
-                    } else {
-                        new_flashblock = true;
-                    }
-                }
+                Ok(flashblock) => match this.blocks.insert(flashblock) {
+                    Ok(_) => this.rebuild = true,
+                    Err(err) => debug!(%err, "Failed to prepare flashblock"),
+                },
                 Err(err) => return Poll::Ready(Some(Err(err))),
             }
         }
@@ -216,16 +214,16 @@ where
             }
         }
 
-        if !new_flashblock && this.current.is_none() {
-            // no new flashbblocks received since, block is still unchanged
-            return Poll::Pending
+        if !this.rebuild && this.current.is_some() {
+            return Poll::Pending;
         }
 
         // try to build a block on top of latest
         match this.execute() {
             Ok(Some(new_pending)) => {
                 // built a new pending block
                 this.current = Some(new_pending.clone());
+                this.rebuild = false;
                 return Poll::Ready(Some(Ok(Some(new_pending))));
             }
             Ok(None) => {