Fix signal handling for Windows compatibility in wapiti.py

[Havoc199x]

This pull request addresses a compatibility issue with Windows by modifying the signal handling in wapiti.py. The following changes were made:

• Conditional Signal Handling: Added a platform check to ensure that signal handling is only applied on non-Windows systems, preventing the NotImplementedError that occurs on Windows when trying to use asyncio signal handlers.

Background

• In Wapiti 3.2, attempting to run the program on Windows results in a NotImplementedError due to the loop.add_signal_handler() function, which is unsupported on Windows. This PR ensures compatibility by conditionally adding signal handlers only on systems where it’s supported (e.g., Linux and macOS).

Testing

• The changes were tested on a Windows system to confirm that they prevent the error and allow Wapiti to run as expected.

Impact

• This change improves cross-platform compatibility, enabling Windows users to use Wapiti without encountering runtime errors related to signal handling.