[BUG] App process doesn't terminate correctly on MacOS

[thatfloflo]

Describe the bug
On recent versions of MacOS with Python 3.10.10 (and possibly other versions), the app doesn't terminate correctly.

It throws a ValueError saying that the event loop has already been destroyed and thus cannot be destroyed, yet the event loop stays alive and the app doesn't terminate.

This might be connected to libev on *nix and to something upstream with eel, but definitely needs further investigating and fixing.

The only current remedy is to send a KeyboardInterrupt (e.g. Ctrl+C) or kill the process manually to completely exit the app. Users can also close the Terminal window, which will prompt them to terminate the process.

To Reproduce
Steps to reproduce the behavior:

1. Follow the User Guide instructions to run as a Python package on MacOS
2. Launch the app in the terminal
3. Close the frontend Chrome window
4. See error

Expected behavior
Exit cleanly once all websocket connections have been closed and the timeout has passed.

System information:

• Device: MacBook
• OS: MacOS / Darwin
• Version: Any

[thatfloflo]

Related issue on Linux is now fixed in 48f23a1, needed a different way of killing Gevent's GHub. I think that would've also done it for MacOS, but that needs confirming before closing this issue.

[thatfloflo]

Recent testing on a MacBook shows this still doesn't exit cleanly on MacOS. May still miss an intercept for some signals and needs more in-depth investigation on a physical Apple device.

[thatfloflo]

As of fbb4fe4 on MacOS Monterey 12.7.5 on a Late 2014 Mac mini, I cannot reproduce the problematic behaviour. Everything looks and feels okay (if not quite ideal due to some other MacOS stuff). We should check this on one or two more machines and then close if it cannot be reproduced anymore.