feat: Make Page.parsed_page the only source of truth for text cells, add OCR cells to it (#1745)

* Keep page.parsed_page.textline_cells and page.cells in sync, including OCR

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

* Make page.parsed_page the only source of truth for text cells

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

* Small fix

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

* Correctly compute PDF boxes from pymupdf

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

* Use different OCR engine order

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

* Add type hints and fix mypy

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

* One more test fix

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

* Remove with pypdfium2_lock from caller sites

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

* Fix typing

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

---------

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

docling/datamodel/base_models.py

@@ -232,7 +232,6 @@ class Page(BaseModel):
     page_no: int
     # page_hash: Optional[str] = None
     size: Optional[Size] = None
-    cells: List[TextCell] = []
     parsed_page: Optional[SegmentedPdfPage] = None
     predictions: PagePredictions = PagePredictions()
     assembled: Optional[AssembledUnit] = None
@@ -245,6 +244,14 @@ class Page(BaseModel):
         float, Image
     ] = {}  # Cache of images in different scales. By default it is cleared during assembling.
 
+    @property
+    def cells(self) -> List[TextCell]:
+        """Return text cells as a read-only view of parsed_page.textline_cells."""
+        if self.parsed_page is not None:
+            return self.parsed_page.textline_cells
+        else:
+            return []
+
     def get_image(
         self, scale: float = 1.0, cropbox: Optional[BoundingBox] = None
     ) -> Optional[Image]: