Return a set of non-conditional runs of "op" nodes with the given names.
For example, "... h q; cx q,q; cx q,q; h q; .." would produce the tuple of cx nodes as an element of the set returned from a call to collect_runs(["cx"]). If instead the cx nodes were "cx q,q; cx q,q;", the method would still return the pair in a tuple. The namelist can contain names that are not in the circuit's basis.
Nodes must have only one successor to continue the run.