feat: Add adaptive OCR, factor out treatment of OCR areas and cell filtering (#38)

* Introduce adaptive OCR

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

* Factor out BaseOcrModel, add docling-parse backend tests, fixes

* Make easyocr default dep

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

---------

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

docling/backend/abstract_backend.py

@@ -18,6 +18,10 @@ class PdfPageBackend(ABC):
     def get_text_cells(self) -> Iterable["Cell"]:
         pass
 
+    @abstractmethod
+    def get_bitmap_rects(self, scale: int = 1) -> Iterable["BoundingBox"]:
+        pass
+
     @abstractmethod
     def get_page_image(
         self, scale: int = 1, cropbox: Optional["BoundingBox"] = None