fix: always return a new bbox when changing origin (#128)

Signed-off-by: Michele Dolfi <[email protected]>

Author: dolfim-ibm

docling_core/types/doc/base.py

@@ -150,7 +150,7 @@ def to_bottom_left_origin(self, page_height: float) -> "BoundingBox":
 
         """
         if self.coord_origin == CoordOrigin.BOTTOMLEFT:
-            return self
+            return self.model_copy()
         elif self.coord_origin == CoordOrigin.TOPLEFT:
             return BoundingBox(
                 l=self.l,
@@ -167,7 +167,7 @@ def to_top_left_origin(self, page_height: float) -> "BoundingBox":
 
         """
         if self.coord_origin == CoordOrigin.TOPLEFT:
-            return self
+            return self.model_copy()
         elif self.coord_origin == CoordOrigin.BOTTOMLEFT:
             return BoundingBox(
                 l=self.l,