[Refactor] implement the guidellm.mock_server package #341
Description
Add a new mock_server for testing and performance validations of the GuideLLM system with a Sanic server that mocks the common OpenAI/vLLM routes
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Add a new mock_server for testing and performance validations of the GuideLLM system with a Sanic server that mocks the common OpenAI/vLLM routes