feat: add tests and integrate dots.ocr model

G.2.5 - Tests:
- Add pytest test suite with fixtures
- test_preprocessing.py - PDF/image loading, normalization, validation
- test_postprocessing.py - chunks, QA pairs, markdown generation
- test_inference.py - dummy parser and inference functions
- test_api.py - API endpoint tests
- Add pytest.ini configuration

G.1.3 - dots.ocr Integration:
- Update model_loader.py with real model loading code
  - Support for AutoModelForVision2Seq and AutoProcessor
  - Device handling (CUDA/CPU/MPS) with fallback
  - Error handling with dummy fallback option
- Update inference.py with real model inference
  - Process images through model
  - Generate and decode outputs
  - Parse model output to blocks
- Add model_output_parser.py
  - Parse JSON or plain text model output
  - Convert to structured blocks
  - Layout detection support (placeholder)

Dependencies:
- Add pytest, pytest-asyncio, httpx for testing

services/parser-service/tests/test_inference.py

@@ -0,0 +1,53 @@
+"""
+Tests for inference functions
+"""
+
+import pytest
+from PIL import Image
+
+from app.runtime.inference import (
+    parse_document_from_images,
+    dummy_parse_document_from_images
+)
+from app.core.config import settings
+
+
+class TestDummyParser:
+    """Tests for dummy parser"""
+    
+    def test_dummy_parse_document_from_images(self):
+        """Test dummy parser with images"""
+        images = [
+            Image.new('RGB', (800, 600), color='white'),
+            Image.new('RGB', (800, 600), color='white')
+        ]
+        
+        doc = dummy_parse_document_from_images(images, doc_id="test-doc")
+        
+        assert doc.doc_id == "test-doc"
+        assert len(doc.pages) == 2
+        assert all(len(page.blocks) > 0 for page in doc.pages)
+        assert all(page.width == 800 for page in doc.pages)
+        assert all(page.height == 600 for page in doc.pages)
+
+
+class TestParseDocumentFromImages:
+    """Tests for parse_document_from_images"""
+    
+    def test_parse_document_from_images_dummy_mode(self, monkeypatch):
+        """Test parsing with dummy mode enabled"""
+        monkeypatch.setenv("USE_DUMMY_PARSER", "true")
+        from app.core.config import Settings
+        settings = Settings()
+        
+        images = [Image.new('RGB', (800, 600), color='white')]
+        doc = parse_document_from_images(images, doc_id="test-doc")
+        
+        assert doc.doc_id == "test-doc"
+        assert len(doc.pages) == 1
+    
+    def test_parse_document_from_images_empty(self):
+        """Test parsing with empty images list"""
+        with pytest.raises(ValueError, match="No valid images"):
+            parse_document_from_images([], doc_id="test-doc")
+