CIF/BDD: Add 'repeat' variable orderer for advanced variable ordering configuration

Currently, variable ordering algorithms can be sequence using an arrow (->). If you want to repeat the same algorithms multiple times you would have to explicitly sequence them all. For example, if you want to apply dcsh, force, and slidwin three times you would have to write it as:

dcsh -> force -> slidwin(effect=both) -> dcsh -> force -> slidwin(effect=both) -> dcsh -> force -> slidwin

It would be nice if there was a repeat option where you can specify a sequence, how many times you would like to repeat it, and the effect. Using such a repeat function, the previous example would look like:

repeat((dcsh -> force -> slidwin), 3, effect=both)

This change would make it easier for developers to create advanced variable ordering configurations and could help future research in finding better variable ordering configurations.