Add `sydTest'` that returns the test tree

[srid]

Basically, this function is useful to implement post-processing tasks like https://github.com/Plutonomicon/plutarch/issues/389

-- | Like `sydTest` but returns the test tree.
sydTest' :: MonadIO m => Spec -> m [SpecTree ()]
sydTest' spec = do
  config <- liftIO $ getSettings
  resultForest <- liftIO $ timedValue <$> sydTestResult config spec
  if shouldExitFail config resultForest
    then liftIO $ exitWith (ExitFailure 1)
    else pure $ void <$> resultForest

Alternatively, I propose making sydTestWith return the tree if backwards compact is unimportant.

[NorfairKing]

I'd like to see how this is used before we consider adding it to sydtest.

[srid]

https://github.com/Plutonomicon/plutarch/pull/390

[NorfairKing]

This is the first time that it comes in handy that sydtest is also a library. Let's see if anyone else would have needed this.

[NorfairKing]

Closing until anyone else needs this.