Introduce an {:isolate_branches} attribute that can be used at the method level

[keyboardDrummer]

{:isolate_branches} would provide a weaker form of {:isolate_assertions}, by only creating a separate VC for each branch in the method. This way, different branches of the same conditional construct would be isolated. Not doing so can lead to rather surprising verification behavior, where changes in one branch effecting the verification of a sibling branch.

We could consider making {:isolate_branches} the default, since it is relatively cheap compared to {:isolate_assertions}.