Limiting scope of signal handling based on environment

[bennothommo]

• Do not handle Linux signals if the PCNTL extension is unavailable. Artisan commands can still function without this extension - they just simply cannot handle termination signals. This prevents commands from throwing an error due to the missing SIGINT/SIGTERM/SIGQUIT constants.
• Prevent multiple registrations of the Windows signal handler if the method is called multiple times.
• Remove specific checks for Windows signals - the handler only accepts two types of signals (CTRL+C or CTRL+BREAK) and both are termination signals.

Summary by CodeRabbit

Release Notes

• Bug Fixes
  • Improved signal handler registration and cleanup mechanisms for more reliable application termination behavior across Windows and Unix-like systems.

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