Add halfspace check to plane

csg/src/plane.rs

@@ -23,6 +23,10 @@ impl Plane {
         }
     }
 
+    pub fn point_in_halfspace(&self, point: Vec3) -> bool {
+        self.normal.dot(point) - self.offset <= math::EPSILON
+    }
+
     pub fn into_vec4(&self) -> Vec4 {
         glam::vec4(self.normal.x, self.normal.y, self.normal.z, -self.offset)
     }