Add assertion for adding multiple Sweeps to a single SweepAdder object
When adding multiple
Sweeps to a single
SweepAdder object (e.g.
timeloop.add() << Sweep(A) << Sweep(B);), none of the
Sweeps is actually added to the timeloop.
Since the user is not informed about this, debugging can be very tedious.
With this MR, these situations are caught and the execution is aborted.