Validate and sanitize SignInit arguments

After the execution of the protocol is completed from every worker, process the results.

1. Aggregate results from all threads
2.1. If the results are valid, send protocol result
2.2. If the results are not valid, send an error message and close the stream

1. creates the first Traffic In message to initiate Sign
2. receives all Traffic Out or every round from a participant and forwards it to all other participants as Traffic In.