Maybe adding chisel3.Driver.apply()

**Type of issue**: feature request

the Driver for chisel3.iotester has an apply method to run the test when we need no parameters. For parameters, we call execute().

The chisel3.Driver needs an execute() method, even when we do not need parameters. Would it make sense to have an apply method here as well (for symmetry)?

Start by locating the chisel3.Driver and chisel3.iotester.Driver entry points, then compare their apply and execute APIs. Clarify the desired parameterless behavior and verify the existing execution paths; done means chisel3.Driver offers the requested symmetric API without changing parameterized execution.

Written by the indexing model from the issue text.