fix: override cancelScheduledDelayedEvent/restart/send in CallWidgetDriver

The base WidgetDriver throws Failed to override function for these
methods. ClientWidgetApi routes update_delayed_event widget actions to
cancelScheduledDelayedEvent, restartScheduledDelayedEvent, or
sendScheduledDelayedEvent. Without these overrides every delayed-event
refresh from element-call fails, causing MembershipManager to drop the
call after retries.

Also make listenAction auto-call preventDefault so io.element.join and
other custom widget actions return success. Add set_always_on_screen
handler so element-call PiP requests are acknowledged.

src/app/plugins/call/CallWidgetDriver.ts

@@ -148,6 +148,18 @@ export class CallWidgetDriver extends WidgetDriver {
     await client._unstable_updateDelayedEvent(delayId, action);
   }
 
+  public async cancelScheduledDelayedEvent(delayId: string): Promise<void> {
+    await this.mx._unstable_cancelScheduledDelayedEvent(delayId);
+  }
+
+  public async restartScheduledDelayedEvent(delayId: string): Promise<void> {
+    await this.mx._unstable_restartScheduledDelayedEvent(delayId);
+  }
+
+  public async sendScheduledDelayedEvent(delayId: string): Promise<void> {
+    await this.mx._unstable_sendScheduledDelayedEvent(delayId);
+  }
+
   public async sendToDevice(
     eventType: string,
     encrypted: boolean,