Flip the SSA safety checks to be opt-in

[TomAFrench]

As mentioned in #7060, these safety checks are taking up a significant portion of compilation time and prevent some of the protocol circuits from being able to be compiled at all.

We don't need to run these checks on every compilation, instead they should be opt-in when the developer is compiling their final circuit and wants to spend time to catch potential bugs which may still be lurking.

[rkarabut]

I would try first to make just the lookback feature opt-in. It doesn't seem to catch a lot of bugs but it's probable that it's the main contributor to the performance hit.