Possible fix for the missing shadows

Try inserting the following statements to the RenderEngine class color_at() method after line 125 of the engine.py module:

# Test if to_light ray hits another object before reaching the light.
(dist, hit) = self.find_nearest(to_light, scene)
if hit is None or (dist > (light.position - hit_pos).magnitude()):

and indent the subsequent "Diffuse and Specular shading" code blocks underneath the newly inserted if statement.

ref: "Shadow Rays" slides in https://www.inf.ed.ac.uk/teaching/courses/cg/lectures/slides10.pdf

Open engine.py and inspect RenderEngine.color_at() around line 125, along with find_nearest() and the surrounding Diffuse and Specular shading blocks. Use the linked Shadow Rays slides for context. Done means the renderer accounts for objects between a surface point and the light when producing shadows.

Written by the indexing model from the issue text.