add parallel llm call demo

[adilhafeez]

✗ uv run main.py
user prompt:  Hello!
assistant response:  Hello! How can I assist you today?
logs: request time: 0.739s, model name: gpt-4o-mini-2024-07-18

user prompt:  Tell me a joke.
assistant response:  Why don't skeletons fight each other? 

They don't have the guts!
logs: request time: 0.799s, model name: gpt-4o-mini-2024-07-18

user prompt:  Who was the president of the United States in the 1990?
assistant response:  In 1990, the President of the United States was George H. W. Bush. He served as the 41st president from January 20, 1989, to January 20, 1993.
logs: request time: 1.346s, model name: gpt-4o-mini-2024-07-18