Adding to Mathics3 signal handling and going into an interactive SIGINT handler

[rocky]

For handling TimeConstrained in systems like pyodide, we should consider adding a SIGALRM signal handler.

As mentioned in #1160 (comment) pyodide can probably send Python signals.

Another use for signal handling is for SIGINT to go break the current execution and go into in interactive mode mid-computation.

Consider also having Breakpoint[] hook into such an interactive signal hander.