Monad constraint on `f` is unnecessarily powerful in many functions

[thomashoneyman]

Several functions in the library require a Monad f constraint where the constraint is unnecessary:

purescript-machines/src/Data/Machine/Mealy.purs

Lines 117 to 119 in d558e0e

	-- | Execute (unroll) a single step on a machine.
	stepMealy :: forall f s a. (Monad f) => s -> MealyT f s a -> f (Step f s a)
	stepMealy = flip runMealyT

purescript-machines/src/Data/Machine/Mealy.purs

Lines 148 to 152 in d558e0e

	take :: forall f s a. (Monad f) => Int -> MealyT f s a -> MealyT f s a
	take n m = if n <= 0 then halt
	else mealy $ \s -> f <$> stepMealy s m
	where f Halt = Halt
	f (Emit a m') = Emit a (take (n - 1) m')

For some of these there is no constraint necessary, and for others something weaker like Applicative would do; perhaps due to functions used internally these really do eventually need the constraint and so it's here for convenience, but if not we could relax them.