Address unresolved code review comments in device_interactor PR

[Copilot]

Applied fixes for three unresolved code review comments from PR #140:

• Removed unused imports: Cleaned up threading and Callable imports from testing/test/light_test.py
• Moved module-level import: Relocated re import to top of device_interactor.py per Python conventions
• Added commissioning window failure handling: Device registration now raises RuntimeError if commissioning window fails to open when open_commissioning_window=True, preventing silent failures during multi-admin setup

if open_commissioning_window:
    result, new_code = self._open_commissioning_window(...)
    if not result.success:
        raise RuntimeError(
            f"Failed to open commissioning window on node {node_id}: {result.stderr}"
        )

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[github-actions]

Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution. You can sign the CLA by just posting a Pull Request Comment same as the below format.

---

I have read the CLA Document and I hereby sign the CLA

---

_{You can retrigger this bot by commenting recheck in this Pull Request. Posted by the CLA Assistant Lite bot.}