feat: up triangle, point-plane distance, exact camera size

[yxlao]

Notes on API change after this PR:

disable_up_triangle=False has been replaced by up_triangle=True in the new API.

Up triangle

Now, we draw the "up triangle" by default, similar to Blender. The up direction is the negative Y direction per OpenCV convention. You may set disable_up_triangle=True to suppress drawing the up triangle.

Absolute camera scale

The camera frame now has an absolute scale, defined by the distance from the camera center to the visualized image plane. E.g., if you set the size to 1, you will get a camera frame where the distance between its camera center and the visualized image plane is 1.

Image width/height for camera plotter

Now, we support specifying image_wh when plotting camera frames. This is useful when the camera center is not exactly at the center of the image plane.

Point to plane distance

Now we can compute point-to-plane distance, where the plane is represented by 3 points. See ct.solver.point_plane_distance_three_points().