…detection

- Updated the condition to detect concave vertices:
  If the z component of the cross product is less than or equal to zero,
  the triangle is considered concave, indicating that the angle between the vectors is greater than 180 degrees.

- Improved the condition to detect flat triangles:
  If the norm (length) of the cross product is close to zero, the vectors are collinear, making the triangle flat with no area.

- Added detailed comments to explain the conditions for concave and flat triangles for better readability and maintainability.