pipebox: improve signal handling

Improve the handling of signals by leveraging the `Py_AtExit`
functionality to trigger cleanup when the interpreter exits.
When receiving SIGINT handle it specially because exceptions in python
are only thrown when the interpreter is running and not when C code is.

python/revng/internal/pipebox.py

@@ -26,8 +26,6 @@ def initialize(argv: list[str] = []):
             signal.SIGTERM,
             signal.SIGHUP,
             signal.SIGQUIT,
-        },
-        {
             signal.SIGCHLD,
             signal.SIGPIPE,
             signal.SIGUSR1,