Simplify detection async methods within MethodCase.
Move MethodCase.Execute(...) to ClassFixture so that all of the fixture lifecycle is in one place, to ease upcoming refactoring.
Refactor away early return statements from ClassFixture.Execute(...).
ExceptionList is an append-only list of exceptions, describing the results of a single case.
Refactor ClassFixture case execution lifecycle to separate the high-level sequence of events from the low-level exception handling of each step.