fix: wait for context should respect already existing contexts (#2998)

This should address Puppeteer test failures:
https://github.com/GoogleChromeLabs/chromium-bidi/actions/runs/12827546451/job/35769733285?pr=2993

Tested manually. 1000 times run Puppeteer test "[locator.spec] Locator
Locator.prototype.filter should resolve as soon as the predicate
matches" with and without the change. Problem is gone.

src/bidiMapper/modules/context/BrowsingContextStorage.ts

@@ -79,6 +79,10 @@ export class BrowsingContextStorage {
   waitForContext(
     browsingContextId: BrowsingContext.BrowsingContext,
   ): Promise<BrowsingContextImpl> {
+    if (this.#contexts.has(browsingContextId)) {
+      return Promise.resolve(this.getContext(browsingContextId));
+    }
+
     return new Promise((resolve) => {
       const listener = (event: {browsingContext: BrowsingContextImpl}) => {
         if (event.browsingContext.id === browsingContextId) {