RFC: Nested failures fail, not raise

[exterm]

We've been using this library for years, but only recently started adopting call! for fast failures.

We found that the behavior of a nested call! vs a fail! was surprising.

E.g.

class SomeInteractor
  include Interactor
  
  def call
    context.fail!
  end
end

SomeInteractor.tap(&:call).failure?

# => true

But,

class NestedInteractor
  include Interactor
  
  def call
    context.fail!
  end
end

class SomeInteractor
  include Interactor
  
  def call
    NestedInteractor.call!
  end
end

SomeInteractor.tap(&call).failure?
# raises Interactor::Failure exception

We would have expected that SomeInteractor.call shows the same behavior in both cases, catching Failure and returning a context with failure status.

I've attached a (very rough) example implementation in this PR.

[dgmora]

@gaffneyc I've been running the last released version and I had some issues with nested interactors. If you use call! inside of the call of an interactor, when the inner interactor fails, the Interactor::Failure gets swallowed and the outer call succeeds.

With #170 it's a bit better, Interactor::Failure is raised. I would expect however, that it behaves as if fail! is called. I've tried this PR and it behaves as I would expect. Is this something that you could consider adding?