Implement 5s timeout for ConPTY handoff embedding.

[Kuldeep2822k]

Add a timer in WindowEmperor to automatically exit after 5 seconds if no windows are created during a ConPTY handoff. The timer is cancelled as soon as a new window is created. This prevents the process from staying alive indefinitely if a handoff fails or is never received.

Summary of the Pull Request

I've implemented a 5-second timeout for the ConPTY handoff embedding in the Windows Terminal.

1. Added a SafeDispatcherTimer _handoffTimeoutTimer; member to the WindowEmperor class.
2. In HandleCommandlineArgs, when the application is launched with the -Embedding flag (ConPTY handoff), the timer is started with a 5-second interval.
3. If the timer ticks (indicating no window was created within 5 seconds), it calls _postQuitMessageIfNeeded() to attempt an application exit.
4. In CreateNewWindow, the timer is explicitly stopped to ensure that the application doesn't exit if a window is successfully created.

The implementation follows the existing codebase patterns using SafeDispatcherTimer and _postQuitMessageIfNeeded

References and Relevant Issues

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

PR Checklist

• Closes #xxx
• Tests added/passed
• Documentation updated
  • If checked, please file a pull request on our docs repo and link it here: #xxx
• Schema updated (if necessary)

[Kuldeep2822k]

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[lhecker]

How did you test this?

[Kuldeep2822k]

How did you test this?

I tested this by launching wt.exe -Embedding without sending a handoff signal. The process (PID 18960) exited automatically after ~5 seconds, confirming the SafeDispatcherTimer fires and calls _postQuitMessageIfNeeded() correctly. Without this fix, the process would remain alive indefinitely.