feat: add pytest testing infrastructure

- Add test optional dependencies to pyproject.toml
- Add conftest.py with fixtures for mocking settings and MCP client
- Add test_server.py with tests for tryton_call and MCP tools

tests/conftest.py

@@ -0,0 +1,25 @@
+import pytest
+import pytest_asyncio
+from unittest.mock import MagicMock, patch
+from fastmcp import Client
+
+
+@pytest.fixture
+def mock_settings():
+    with patch("tryton_mcp.server.settings") as mock:
+        mock_client = MagicMock()
+        mock.get_client.return_value = mock_client
+        yield mock
+
+
+@pytest.fixture
+def mcp_server():
+    from tryton_mcp.server import mcp
+
+    return mcp
+
+
+@pytest_asyncio.fixture
+async def mcp_client(mcp_server):
+    async with Client(mcp_server) as client:
+        yield client