Integrate FastMCP

This commit integrates FastMCP, a high-level MCP server implementation originally written by Jeremiah Lowin,
into the official MCP SDK. It also updates dependencies and adds new dev dependencies.
It moves the existing SDK into a .lowlevel .

tests/conftest.py

@@ -27,3 +27,7 @@ def mcp_server() -> Server:
         ]
 
     return server
+
+@pytest.fixture
+def anyio_backend():
+    return 'asyncio'