Add comprehensive tests for all geo GraphQL endpoints

Created test suite covering all 8 main geo service endpoints:
- Basic: products, nodes (with filters/bounds), clusteredNodes
- Nearest: nearestHubs, nearestOffers, nearestSuppliers (with product filters)
- Routing: routeToCoordinate, autoRoute, railRoute
- Edge cases: invalid coordinates, zero radius, nonexistent UUIDs

Test suite uses real API calls to production GraphQL endpoint.
16 tests total across 4 test classes.

Files:
- tests/test_graphql_endpoints.py: Main test suite (600+ lines)
- tests/README.md: Documentation and usage guide
- pytest.ini: Pytest configuration
- run_tests.sh: Convenience script to run tests
- pyproject.toml: Added pytest and requests as dev dependencies

tests/__init__.py

@@ -0,0 +1 @@
+# Geo service tests