fix(py): forward api_key kwargs to litellm validation

[vincent067]

Hi there! 👋

This PR fixes #190 — api_key passed via kwargs was being dropped during validation in the Python SDK.

What was broken

Currently, if you pass api_key directly to zerox():

result = await zerox(
    file_path="doc.pdf",
    model="gpt-4o-mini",
    api_key="sk-xxx"  # passed via kwargs
)

…it still fails with:

MissingEnvironmentVariables: missing_keys: ['OPENAI_API_KEY']

That happens because litellm.validate_environment() and litellm.check_valid_key() both support an api_key parameter, but litellmmodel was never forwarding it.

The fix

Two small changes in py_zerox/pyzerox/models/modellitellm.py:

1. validate_environment — now passes api_key=self.kwargs.get(\"api_key\") to litellm.validate_environment()
2. validate_access — now passes api_key=self.kwargs.get(\"api_key\") to litellm.check_valid_key() instead of hard-coding None

This makes per-request API key injection work as expected, which is important for multi-tenant apps and testing environments where global env vars aren't desirable.

Let me know if you'd like any tweaks — happy to iterate! 😊