Add `ActionState::Finally` that always runs

[ndarilek]

I have actions that can succeed or fail. Independently of that, they generally need to run some cleanup to ensure that scorers know what has already been handled.

It'd be nice if actions first ran with ActionState::Success or ActionState::Failure, then an ActionState::Final match could handle all my cleanup. Now I'm performing all my cleanup in Success or Failure arms which is a bit confusing, particularly if I want a failure case but don't want to repeat the cleanup.

Thanks!

[zkat]

I can't think of a good way to implement this that doesn't make Actions dependent on definitely catching a single-frame run.

[ekalosak]

Maybe close as inactive? Or the author could sketch an implementation for feedback?