Implement watchdogs

[enrique-tyris]

Please just add an optionally configurable timer to each state. Useful for avoiding the machine infinitely getting stuck on certain state.

Quite a pain in the ass to implement manually, tried usign ThreadPoolExecutor but then thread context is ruined and before_ and after_ transition methods do not work.

[fgmacedo]

Hi @enrique-tyris , thanks for your suggestion.

Implemented on #585.

It will land on v3.0! 🚀

Best regards!

[enrique-tyris]

Thanks @fgmacedo, you're great!!