fix: free handles after stop (Windows)

[hut36]

Free handles after stop so that wen can do prevent_display_sleep after stop.

---

Note

Close Windows power request handles on stop, reset internal state, add drop-based cleanup, and test restarting after stop.

• Windows handle management:
  • Replace PowerClearRequest with CloseHandle for both system_handle and optional display_handle in nosleep-windows/src/lib.rs.
  • Clear internal state by setting self.no_sleep_handle = None after closing.
• Lifecycle:
  • Implement Drop for NoSleep to automatically call stop().
• Tests:
  • Add test_start_after_stop to verify starting after stop().
• Imports:
  • Add CloseHandle to windows::Win32::Foundation and remove unused power-clear import.

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[pevers]

Thanks for taking the time to fix this! I've a small suggestion to implement it as Drop.

[hut36]

@pevers, thanks for review! I've updated the PR.

[pevers]

Looks good! Thank you!