fix(openaicaller.py): fix import statement for num_tokens_from_messages function
refactor(openaicaller.py): remove unused api_key parameter from openai_caller class constructor
refactor(openaicaller.py): change generate_response and moderation methods to accept variable number of arguments
refactor(openaicaller.py): change error_call parameter to be optional and provide a default function if not provided
refactor(openaicaller.py): remove unused api_key parameter from generate_response and moderation methods
refactor(openaicaller.py): remove unused api_key parameter from main function