fix(client): do not spam public lobbies requests by waiting for previous request to end before firing a new one (#2276)

## Description:

This PR aims to (quickly, not definitely) address
https://github.com/openfrontio/OpenFrontIO/issues/2274 as I believe
that's an urgent DDOS problem with the frontend design.

I am looking at the backend to understand the underlying issue.

## How was this tested:

I added a 2 seconds "sleep" to the endpoint `public_lobbies` to simulate
loads.

The frontend would do request every seconds, which kept piling up on the
server and decreased performances, cf screenshot, instead of resolving
every 2 seconds, each subsequent request would take longer than the
previous one.
<img width="849" height="263" alt="Screenshot 2025-10-23 at 23 36 37"
src="https://github.com/user-attachments/assets/31ded504-a72e-4794-9c5e-b9b0c675dd33"
/>

After adding the fix to the frontend (which can only trigger 1 request
at a time, waiting for the previous one), all request completed in
approximatively 2 seconds as expected, cf screenshot.

<img width="849" height="263" alt="Screenshot 2025-10-23 at 23 36 54"
src="https://github.com/user-attachments/assets/bc680642-407a-4a55-aeed-6a03bad35327"
/>

 
## 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:

sorikairo

Co-authored-by: Vivacious Box <jon@rouillard.org>

src/client/PublicLobby.ts

@@ -17,6 +17,7 @@ export class PublicLobby extends LitElement {
   private currLobby: GameInfo | null = null;
   private debounceDelay: number = 750;
   private lobbyIDToStart = new Map<GameID, number>();
+  private lobbiesFetchInFlight: Promise<GameInfo[]> | null = null;
 
   createRenderRoot() {
     return this;
@@ -73,16 +74,26 @@ export class PublicLobby extends LitElement {
   }
 
   async fetchLobbies(): Promise<GameInfo[]> {
-    try {
-      const response = await fetch(`/api/public_lobbies`);
-      if (!response.ok)
-        throw new Error(`HTTP error! status: ${response.status}`);
-      const data = await response.json();
-      return data.lobbies;
-    } catch (error) {
-      console.error("Error fetching lobbies:", error);
-      throw error;
+    if (this.lobbiesFetchInFlight) {
+      return this.lobbiesFetchInFlight;
     }
+
+    this.lobbiesFetchInFlight = (async () => {
+      try {
+        const response = await fetch(`/api/public_lobbies`);
+        if (!response.ok)
+          throw new Error(`HTTP error! status: ${response.status}`);
+        const data = await response.json();
+        return data.lobbies as GameInfo[];
+      } catch (error) {
+        console.error("Error fetching lobbies:", error);
+        throw error;
+      } finally {
+        this.lobbiesFetchInFlight = null;
+      }
+    })();
+
+    return this.lobbiesFetchInFlight;
   }
 
   public stop() {