perf(core): reduce packed tile update churn (#3253)

## Description:
- Build packedTileUpdates directly into a BigUint64Array (avoid
intermediate JS array + copy).

- Transfer packedTileUpdates.buffer in worker postMessage to avoid
structured-clone.


- Avoids large short-lived allocations during tile-update (lower peak
heap and GC pressure).
- Prevents duplicating buffers across thread boundaries when the main
thread is behind. (one buffer per queued update, not two)

**Notes**

- after postMessage(..., [packedTileUpdates.buffer]) transfer the
worker’s packedTileUpdates becomes unusable (its .buffer is detached).


- [ ] I have added screenshots for all UI updates
- [ ] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [ ] I have added relevant tests to the test directory
- [ ] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

DISCORD_USERNAME

src/core/GameRunner.ts

@@ -173,12 +173,16 @@ export class GameRunner {
     }
 
     // Many tiles are updated to pack it into an array
-    const packedTileUpdates = updates[GameUpdateType.Tile].map((u) => u.update);
+    const tileUpdates = updates[GameUpdateType.Tile];
+    const packedTileUpdates = new BigUint64Array(tileUpdates.length);
+    for (let i = 0; i < tileUpdates.length; i++) {
+      packedTileUpdates[i] = tileUpdates[i].update;
+    }
     updates[GameUpdateType.Tile] = [];
 
     this.callBack({
       tick: this.game.ticks(),
-      packedTileUpdates: new BigUint64Array(packedTileUpdates),
+      packedTileUpdates,
       updates: updates,
       playerNameViewData: this.playerViewData,
       tickExecutionDuration: tickExecutionDuration,

src/core/worker/Worker.worker.ts

@@ -30,6 +30,12 @@ function gameUpdate(gu: GameUpdateViewData | ErrorUpdate) {
 }
 
 function sendMessage(message: WorkerMessage) {
+  if (message.type === "game_update") {
+    // Transfer the packed tile updates buffer to avoid structured-clone copies and
+    // reduce worker-side memory churn during long runs / catch-up.
+    ctx.postMessage(message, [message.gameUpdate.packedTileUpdates.buffer]);
+    return;
+  }
   ctx.postMessage(message);
 }