Add type hints for clarity

[flrs]

We should add type hints to improve clarity regarding inputs and outputs.

[amirothman]

do you have any suggestions for which portion of the code would be most helpful if we were to add type hinting?

[flrs]

Hi @amirothman,

I think type hinting could be useful for all blending functions. For example:

blend_modes/blend_modes/blending_functions.py

Line 73 in 4eca947

def normal(img_in, img_layer, opacity, disable_type_checks: bool = False):

Could be transformed to something like

def normal(
   img_in: np.ndarray,
   img_layer: np.ndarray,
   opacity: float,
   disable_type_checks: bool = False): 

It may be beneficial to be clearer about what kind of numpy arrays we expect, since there are some restrictions:

blend_modes/blend_modes/blending_functions.py

Line 94 in 4eca947

img_in(3-dimensional numpy array of floats (r/g/b/a) in range 0.0-255.0): Layer to be blended with image

It could be worth exploring solutions like https://github.com/ramonhagenaars/nptyping, since I don't think numpy type hints are supported by Python natively at this point.