fix: Do not abort blockstream loop during sync (#10884)

The L2 blockstream is expected to download blocks continuously until
reaching the source's block number. However, to exit from that loop when
the service is stopped, we continuously check for the isRunning flag and
abort if it is not set.

This means that in a sync, which happens outside the running loop, we
end up cutting that loop short. This provides a quick and dirty fix for
that.

yarn-project/circuit-types/src/l2_block_downloader/l2_block_stream.ts

@@ -8,6 +8,7 @@ import { type L2BlockId, type L2BlockSource, type L2Tips } from '../l2_block_sou
 /** Creates a stream of events for new blocks, chain tips updates, and reorgs, out of polling an archiver or a node. */
 export class L2BlockStream {
   private readonly runningPromise: RunningPromise;
+  private isSyncing = false;
 
   constructor(
     private l2BlockSource: Pick<L2BlockSource, 'getBlocks' | 'getBlockHeader' | 'getL2Tips'>,
@@ -37,8 +38,10 @@ export class L2BlockStream {
     return this.runningPromise.isRunning();
   }
 
-  public sync() {
-    return this.runningPromise.trigger();
+  public async sync() {
+    this.isSyncing = true;
+    await this.runningPromise.trigger();
+    this.isSyncing = false;
   }
 
   protected async work() {
@@ -132,7 +135,7 @@ export class L2BlockStream {
       `Emitting ${event.type} (${event.type === 'blocks-added' ? event.blocks.length : event.blockNumber})`,
     );
     await this.handler.handleBlockStreamEvent(event);
-    if (!this.isRunning()) {
+    if (!this.isRunning() && !this.isSyncing) {
       throw new AbortError();
     }
   }