Missing dependencies for test

[jkawamoto]

When I ran tests using this command:

pip install -e ".[test]"
python -m pytest

I got this error message:

    def test_llama_server():
>       from fastapi.testclient import TestClient
E       ModuleNotFoundError: No module named 'fastapi'

tests/test_llama.py:246: ModuleNotFoundError

This PR adds the missing dependencies for the test feature.