fix: replace setInterval with recursive setTimeout in Master.ts to pr… (#2869)

If this PR fixes an issue, link it below. If not, delete these two
lines.
Resolves #2868 

## Description:

This PR addresses a critical memory leak in the Master server process
(causing ~30GB RAM usage).

The issue was caused by `setInterval` calling `fetchLobbies()` every
100ms. When `fetchLobbies` took longer than 100ms to complete (due to
network latency or load), requests would pile up indefinitely, creating
a massive queue of pending Promises and open sockets.

I have refactored the polling logic into a generic `startPolling`
utility (in `src/server/PollingLoop.ts`) that uses a recursive
`setTimeout` pattern. This ensures that the next `fetchLobbies` call is
only scheduled *after* the previous one has completed (successfully or
failed), preventing any request pile-up.

## Please complete the following:

- [x] I have added screenshots for all UI updates (N/A - backend only)
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file (N/A - no user facing text)
- [x] I have added relevant tests to the test directory
(`tests/PollingLoop.test.ts`)
- [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:

codimo

src/server/PollingLoop.ts

@@ -0,0 +1,24 @@
+import { logger } from "./Logger";
+
+const log = logger.child({ comp: "polling" });
+
+/**
+ * Starts a polling loop that executes the given async task effectively recursively using setTimeout.
+ * This guarantees that the next execution only starts after the previous one has completed (or failed),
+ * preventing request pile-ups.
+ *
+ * @param task The async function to execute.
+ * @param intervalMs The delay in milliseconds before the next execution.
+ */
+export function startPolling(task: () => Promise<void>, intervalMs: number) {
+  const runLoop = () => {
+    task()
+      .catch((error) => {
+        log.error("Error in polling loop:", error);
+      })
+      .finally(() => {
+        setTimeout(runLoop, intervalMs);
+      });
+  };
+  runLoop();
+}