Add a realism simulator

[lukehinds]

I expect some might want this for demos with an aspect of realism to the response. If set (cli or env) we could add a random inject into time.sleep to cause modulations of lag in response, especially in stream responses. This would better element an LLM , a slight pause after sending the prompt, followed by a stream 1 to 2 seconds later, with micro lags mid stream.

@danbarr , useful?

[lukehinds]

done: #11