Replace ActorShape as the base class for CloudShape, HexagonShape, and
TriangleShape. These classes had no functional relation with ActorShape -
the inheritance was only for technical convenience.

Introduce AbstractPathShape as a dedicated abstract base class to make
the hierarchy more explicit and semantically clear. ActorShape now extends
AbstractPathShape alongside the other shapes.

Changes:
- Add new AbstractPathShape abstract class
- Refactor ActorShape to extend AbstractPathShape
- Update CloudShape, HexagonShape, and TriangleShape to extend AbstractPathShape