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/conftest.py

@@ -0,0 +1,106 @@
+"""
+Pytest configuration and fixtures
+"""
+
+import pytest
+import os
+from pathlib import Path
+from PIL import Image
+import io
+
+# Test fixtures directory
+FIXTURES_DIR = Path(__file__).parent / "fixtures"
+DOCS_DIR = FIXTURES_DIR / "docs"
+
+
+@pytest.fixture
+def fixtures_dir():
+    """Return fixtures directory path"""
+    return FIXTURES_DIR
+
+
+@pytest.fixture
+def docs_dir():
+    """Return test documents directory path"""
+    return DOCS_DIR
+
+
+@pytest.fixture
+def sample_image_bytes():
+    """Create a sample image in memory"""
+    img = Image.new('RGB', (800, 600), color='white')
+    buffer = io.BytesIO()
+    img.save(buffer, format='PNG')
+    return buffer.getvalue()
+
+
+@pytest.fixture
+def sample_pdf_bytes():
+    """Create a minimal PDF in memory (for testing)"""
+    # Minimal valid PDF structure
+    pdf_content = b"""%PDF-1.4
+1 0 obj
+<<
+/Type /Catalog
+/Pages 2 0 R
+>>
+endobj
+2 0 obj
+<<
+/Type /Pages
+/Kids [3 0 R]
+/Count 1
+>>
+endobj
+3 0 obj
+<<
+/Type /Page
+/Parent 2 0 R
+/MediaBox [0 0 612 792]
+/Contents 4 0 R
+/Resources <<
+/Font <<
+/F1 <<
+/Type /Font
+/Subtype /Type1
+/BaseFont /Helvetica
+>>
+>>
+>>
+>>
+endobj
+4 0 obj
+<<
+/Length 44
+>>
+stream
+BT
+/F1 12 Tf
+100 700 Td
+(Test PDF) Tj
+ET
+endstream
+endobj
+xref
+0 5
+0000000000 65535 f
+0000000009 00000 n
+0000000058 00000 n
+0000000115 00000 n
+0000000306 00000 n
+trailer
+<<
+/Size 5
+/Root 1 0 R
+>>
+startxref
+400
+%%EOF"""
+    return pdf_content
+
+
+@pytest.fixture
+def temp_dir(tmp_path):
+    """Temporary directory for test files"""
+    return tmp_path
+