Working Binary, Fixed Process spawn & termination bug, Fixed callsign hot reload bug

• Processes are now spawned via the multiprocessing API instead of the ProcessPoolExecutor one. I believe this is more robust and reliable.
• Every plugin process spawned, now implements a signal handler for SIGINT that calls exit. This should probably fix these weird issues where the server would not quit unless killed.
• Fixed a logic error in the callsign implementation regarding hot reload/debug.
• The binary submitted, was built by me using local pyinstaller on my Steam Deck, and basic functionality was confirmed working. We ran into weird issues with the Github Action that we use for building, and are looking into a different solution. Until we figure that out, nightly builds will most likely be broken.