Use thread-safe timeout-decorator

[x-way]

When using the checkdmarc module not in the main thread, the (default) implementation of timeout-decorator using signals does not work and fails with an exception.

This change uses the multiprocessing capable implementation of timeout-decorator, so that the checkdmarc module can also be used outside the main thread.

See https://pypi.org/project/timeout-decorator/#multithreading

[seanthegeek]

Unfortunately, I cannot accept this change, because it would break Windows support.

Make sure that in case of multiprocessing strategy for timeout, your function does not return objects which cannot be pickled, otherwise it will fail at marshalling it between master and child processes.

uqfoundation/dill#308

bitranox/wrapt_timeout_decorator#10

[MrKragh]

This is now some years ago. Do you know if this still is an issue on Windows?
I'm currently using this on an Azure Function App that are failing due to being threaded. Have forked it for now, but would love to find a solution making me able to follow this project. Thanks!