This change solves an issue faced by users who aren't intending to use OpenAI getting scary error messages saying that they need the `openai` optional dependency "in order to use OpenAI", along with an instruction to set the OPENAI_API_KEY environment variable.
Note that with this change we could theoretically remove from pyproject.toml a number of defined optional dependencies that list only the `openai` package as a dependency (like `deepseek`, for example), but I didn't want to "break the API" in terms of how users install/consume pipecat and its set of built-in services.
Finally, I removed the `python-deepcompare` dependency from the `openai` optional dependency, since it appears to me like it was added by mistake (my guess is it was used for debugging during development and then never removed).
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