Fix: Catch TargetClosedError in PlaywrightController.sleep() to avoid crashes on download-triggered page closes

[oscarvdl]

Why are these changes needed?

This PR fixes a crash that occurs when using MultimodalWebSurfer in scenarios where a click triggers a file download.
After the download is initiated, Playwright may close the page or context, leading to a TargetClosedError during sleep() in PlaywrightController.

The previous implementation of sleep() did not handle these closures, causing the agent to crash unexpectedly.

This PR adds safe exception handling for TargetClosedError and PlaywrightError during sleep(), ensuring that the agent can continue operating gracefully even if the page closes.

Related issue number

Closes #6413

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.51%. Comparing base (bd3b97a) to head (aaa6233).
⚠️ Report is 149 commits behind head on main.

Files with missing lines	Patch %	Lines
...gen_ext/agents/web_surfer/playwright_controller.py	60.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6415      +/-   ##
==========================================
- Coverage   79.52%   79.51%   -0.01%     
==========================================
  Files         225      225              
  Lines       16624    16627       +3     
==========================================
+ Hits        13220    13221       +1     
- Misses       3404     3406       +2     

Flag	Coverage Δ
unittests	79.51% <60.00%> (-0.01%)	⬇️

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