Implement upstream PR #14862: Target.asPage returns same Page instance (#3410)

Ports puppeteer/puppeteer#14862.
BidiPageTarget/BidiFrameTarget return cached page instead of creating new instance.
CdpPageTarget.AsPageAsync() returns existing PageTask page when available.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: kblok

lib/PuppeteerSharp/Bidi/BidiFrameTarget.cs

@@ -52,8 +52,7 @@ public override Task<IPage> PageAsync()
         return Task.FromResult<IPage>(_page);
     }
 
-    public override Task<IPage> AsPageAsync()
-        => Task.FromResult(BidiPage.From((BidiBrowserContext)_frame.Page.BrowserContext, _frame.BrowsingContext) as IPage);
+    public override Task<IPage> AsPageAsync() => Task.FromResult<IPage>(_frame.Page as BidiPage);
 
     public override Task<ICDPSession> CreateCDPSessionAsync() => throw new PuppeteerException("Not supported");
 }

lib/PuppeteerSharp/Bidi/BidiPageTarget.cs

@@ -41,10 +41,7 @@ internal class BidiPageTarget(BidiPage page) : Target
 
     public override Task<IPage> PageAsync() => Task.FromResult<IPage>(page);
 
-    public override Task<IPage> AsPageAsync()
-#pragma warning disable CA2000
-        => Task.FromResult(BidiPage.From((BidiBrowserContext)page.BrowserContext, page.BidiMainFrame.BrowsingContext) as IPage);
-#pragma warning restore CA2000
+    public override Task<IPage> AsPageAsync() => Task.FromResult<IPage>(page);
 
     public override Task<ICDPSession> CreateCDPSessionAsync()
         => page.CreateCDPSessionAsync();

lib/PuppeteerSharp/Cdp/CdpPageTarget.cs

@@ -29,6 +29,21 @@ internal CdpPageTarget(
 
         internal Task<Page> PageTask { get; set; }
 
+        /// <inheritdoc/>
+        public override async Task<IPage> AsPageAsync()
+        {
+            if (PageTask != null)
+            {
+                var page = await PageTask.ConfigureAwait(false);
+                if (page != null)
+                {
+                    return page;
+                }
+            }
+
+            return await base.AsPageAsync().ConfigureAwait(false);
+        }
+
         /// <inheritdoc/>
         public override async Task<IPage> PageAsync()
         {