Cardinal sensor distances are calculated incorrectly

[nosas]

The function _find_nearest_collision in sensor.py is calculating the distance from the Wall's midpoint. Instead, we should calculate the difference between the Agent's position and y values for North/South and x values for East/West. Like so...

        for obj in self._collisions:
            obj_rect_coord = {
                "N": pg.Vector2(self.agent.pos.x, obj.rect.bottom),
                "S": pg.Vector2(self.agent.pos.x, obj.rect.top),
                "E": pg.Vector2(obj.rect.left, self.agent.pos.y),
                "W": pg.Vector2(obj.rect.right, self.agent.pos.y),
            }

This explains why my Agents were continuously running into walls even though I discouraged that behavior in the GameEnv reward function lol. RL is fun. Agents are good at finding these edge cases.

[nosas]

Tests are required before closing this issue:

1. Test cardinal distances
2. Test cardinal object types

[nosas]

The training map, or even the training process, from issue #27 will be mostly the same