refactor: move llm tests to separate integration and mocked files and centralize fixtures in conftest.py

test/conftest.py

@@ -0,0 +1,17 @@
+import pytest
+from photools3.llm_session import LlmSession
+from photools3.photo import Photo
+from test.test_photo import PATHS_DNG_EXAMPLES
+
+@pytest.fixture
+def test_photo():
+    return Photo(PATHS_DNG_EXAMPLES[0])
+
+@pytest.fixture
+def llm_session():
+    return LlmSession(
+        system_prompt=(
+            "You are a helpful assistent to photographer. "
+            'Answer in JSON format: `{"caption": "...", "tags": ["tag1", "tag2", ...]}`'
+        )
+    )