Feat: advanced markdown parsing (#9607)

### What problem does this PR solve?

Using AST parsing to handle markdown more accurately, preventing
components from being cut off by chunking. #9564

<img width="1746" height="993" alt="image"
src="https://github.com/user-attachments/assets/4aaf4bf6-5714-4d48-a9cf-864f59633f7f"
/>

<img width="1739" height="982" alt="image"
src="https://github.com/user-attachments/assets/dc00233f-7a55-434f-bbb7-74ce7f57a6cf"
/>

<img width="559" height="100" alt="image"
src="https://github.com/user-attachments/assets/4a556b5b-d9c6-4544-a486-8ac342bd504e"
/>


### Type of change

- [x] New Feature (non-breaking change which adds functionality)

deepdoc/parser/__init__.py

@@ -14,13 +14,15 @@
 #  limitations under the License.
 #
 
-from .pdf_parser import RAGFlowPdfParser as PdfParser, PlainParser
 from .docx_parser import RAGFlowDocxParser as DocxParser
 from .excel_parser import RAGFlowExcelParser as ExcelParser
-from .ppt_parser import RAGFlowPptParser as PptParser
 from .html_parser import RAGFlowHtmlParser as HtmlParser
 from .json_parser import RAGFlowJsonParser as JsonParser
+from .markdown_parser import MarkdownElementExtractor
 from .markdown_parser import RAGFlowMarkdownParser as MarkdownParser
+from .pdf_parser import PlainParser
+from .pdf_parser import RAGFlowPdfParser as PdfParser
+from .ppt_parser import RAGFlowPptParser as PptParser
 from .txt_parser import RAGFlowTxtParser as TxtParser
 
 __all__ = [
@@ -33,4 +35,6 @@ __all__ = [
     "JsonParser",
     "MarkdownParser",
     "TxtParser",
-]
+    "MarkdownElementExtractor",
+]
+