feat: add save and load for conversion result (#2648)

* feat: added save_as_json and load_from_json to ConversionResult

Signed-off-by: Peter Staar <taa@zurich.ibm.com>

* added a test

Signed-off-by: Peter Staar <taa@zurich.ibm.com>

* fixed the save and load for ConversionResult

Signed-off-by: Peter Staar <taa@zurich.ibm.com>

* reformatted the code

Signed-off-by: Peter Staar <taa@zurich.ibm.com>

* fixed the signature

Signed-off-by: Peter Staar <taa@zurich.ibm.com>

* refactored load/save into ConversionAssets

Signed-off-by: Peter Staar <taa@zurich.ibm.com>

* added the DoclingVersion class

Signed-off-by: Peter Staar <taa@zurich.ibm.com>

* renamed time_stamp to timestamp

Signed-off-by: Peter Staar <taa@zurich.ibm.com>

---------

Signed-off-by: Peter Staar <taa@zurich.ibm.com>

tests/test_conversion_result_json.py

@@ -0,0 +1,44 @@
+from io import BytesIO
+from pathlib import Path
+
+import pytest
+
+from docling.backend.pypdfium2_backend import (
+    PyPdfiumDocumentBackend,
+    PyPdfiumPageBackend,
+)
+from docling.datamodel.base_models import ConversionStatus, InputFormat
+from docling.datamodel.document import ConversionAssets
+from docling.datamodel.pipeline_options import PdfPipelineOptions
+from docling.document_converter import DocumentConverter, PdfFormatOption
+
+
+def test_conversion_result_json_roundtrip_string():
+    pdf_doc = Path("./tests/data/pdf/redp5110_sampled.pdf")
+
+    pipeline_options = PdfPipelineOptions()
+    pipeline_options.do_ocr = False
+    pipeline_options.images_scale = 1.0
+    pipeline_options.generate_page_images = False
+    pipeline_options.do_table_structure = False
+    pipeline_options.table_structure_options.do_cell_matching = True
+    pipeline_options.generate_parsed_pages = True
+
+    doc_converter = DocumentConverter(
+        format_options={
+            InputFormat.PDF: PdfFormatOption(
+                pipeline_options=pipeline_options, backend=PyPdfiumDocumentBackend
+            )
+        }
+    )
+    conv_res = doc_converter.convert(pdf_doc)
+
+    fpath: Path = Path("./test-conversion.zip")
+
+    conv_res.save(filename=fpath)  # returns string when no filename is given
+    # assert isinstance(json_str, str) and len(json_str) > 0
+
+    loaded = ConversionAssets.load(filename=fpath)
+
+    assert loaded.status == conv_res.status
+    assert loaded.document.name == conv_res.document.name