refactor openai multimodal (#17951)

...s/llama-index-llms-openai/llama_index/llms/openai/base.py

...-integrations/llms/llama-index-llms-openai/pyproject.toml

...-openai/llama_index/multi_modal_llms/azure_openai/base.py

.../llama-index-multi-modal-llms-azure-openai/pyproject.toml

...-azure-openai/tests/test_multi-modal-llms_azure_openai.py

...l_llms/llama-index-multi-modal-llms-nebius/pyproject.toml

...i-modal-llms-nebius/tests/test_multi_modal_llms_nebius.py

...l-llms-openai/llama_index/multi_modal_llms/openai/base.py

...-llms-openai/llama_index/multi_modal_llms/openai/utils.py

...l_llms/llama-index-multi-modal-llms-openai/pyproject.toml

...i-modal-llms-openai/tests/test_multi-modal-llms_openai.py