Adds support for supplying a binPath dynamically

[scalvert]

In some cases, we need to be able to supply the binPath dynamically, such as if the bin is part of a dependency within the Project itself. This is only possible dynamically, since the project is dynamically created and destroyed.

This change widens the type of binPath:

binPath: string | (<TProject extends BinTesterProject>(project: TProject) => string);