fix: add readyState check before endTurn broadcast (#3879)

## Description:

Guard `ws.send()` in `endTurn()` with a `readyState === OPEN` check to
prevent sending messages to WebSocket connections that have already
closed.

Without this guard, broadcasting to a client whose connection closed
between ticks can throw an exception and crash the game loop.

## Please complete the following:

- [X] I have added screenshots for all UI updates
- [X] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [X] I have added relevant tests to the test directory
- [X] 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:

barfires

src/server/GameServer.ts

@@ -823,7 +823,9 @@ export class GameServer {
       turn: pastTurn,
     } satisfies ServerTurnMessage);
     this.activeClients.forEach((c) => {
-      c.ws.send(msg);
+      if (c.ws.readyState === c.ws.OPEN) {
+        c.ws.send(msg);
+      }
     });
   }