Potential Issues with traversal infra, counters

[khosravipasha]

1. foreach_down had some unexpected behaviour
2. reset_counter might not work in all cases

And overall want a more reliable way of reseting the travesals without having to reload the circuit again.

[guyvdbroeck]

I added reset_counter_hard in fbdedf2
It resets the counter even if the nodes' fields are messed up (but is slower than the default implementation).

julia> circuit = load_smooth_logic_circuit(zoo_psdd_file("plants.psdd"));

julia> @btime (reset_counter(circuit,1);reset_counter(circuit,0))
  46.723 ms (0 allocations: 0 bytes)

julia> @btime (reset_counter_hard(circuit,1);reset_counter_hard(circuit,0))
  73.743 ms (540960 allocations: 14.26 MiB)

I believe this closes the issue?