Release: Fixes And Polygon Exit

[mikedh]

• remove the trimesh.triangles.crosses(... sum) argument which was unused internally, unnecessary since you can just call .sum() on the result, and shadowed a built-in function.
• add an early exit for enclosure_tree for inputs with 0 or 1 value
• add another early exit for trimesh.boolean.reduce_cascade for inputs with a single value
• add a "manual" 2D cross product for trimesh.triangles.cross
• release and test Fixes #2195 #2231
• release and test Update transformations.py #2254