API key required even when using local language models

[lostmygithubaccount]

First check

• I added a descriptive title to this issue.
• I used the GitHub search to try to find a similar issue and didn't find one.
• I searched the Marvin documentation for this issue.

Bug summary

one issue is that the BASE_URL option doesn't seem to be documented anywhere -- would be happy to contribute an example after I have this working well

the main bug here is that if I have ~/.marvin/.env like so:

# LOCAL
MARVIN_OPENAI_BASE_URL="http://127.0.0.1:8080/v1"

I get an error (much of the stacktrace omitted for brevity):

[ins] In [1]: import marvin
@
[ins] In [2]: @marvin.fn
         ...: def write_poem() -> str:
         ...:     """Writes a cool poem"""
         ...:

[ins] In [3]: write_poem()
---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)

...

ValueError: OpenAI API key not found! Marvin will not work properly without it.

You can either:
    1. Set the `MARVIN_OPENAI_API_KEY` or `OPENAI_API_KEY` environment variables
    2. Set `marvin.settings.openai.api_key` in your code (not recommended for production)

If you do not have an OpenAI API key, you can create one at https://platform.openai.com/api-keys.

I can easily work around this by setting the MARVIN_OPENAI_API_KEY to any value, but I think ti shouldn't be required (at least if setting the base URL?)

Reproduction

see above

Error

see above

Versions

2.1.3

Additional context

No response

[zzstoatzz]

hi @lostmygithubaccount - good callout, thanks!

#830 improves the handling here