Omit Authorization header when api_key is empty

[devin-ai-integration]

Summary

cohere.Client(api_key="") (and ClientV2/AsyncClient/AsyncClientV2) now sends no Authorization header, so the client can point at a proxy / self-hosted deployment that performs its own auth. A non-empty key — including a callable/async token supplier — behaves exactly as before.

No generated file changes: the patch lives entirely in the already-handwritten, already-.fernignored src/cohere/overrides.py, which wraps the generated header builders at import time:

def patched_get_headers(self):
    headers = get_headers(self)
    if not self._get_token():          # covers str and callable tokens
        headers.pop("Authorization", None)
    return headers

The async variant keys off the rendered value ("Bearer ") because async_get_headers re-sets the header from self._async_token() after get_headers() runs. The patch is idempotent (guarded by BaseClientWrapper._omits_empty_authorization) since run_overrides() can be invoked more than once.

Note on the base branch: this targets upstream-main, a branch I pushed at current cohere-ai/cohere-python main (050f9c0), because this fork's main is from 2024 and conflicts with upstream — that keeps the diff to just these two files. Happy to re-open against a fresh fern-demo/cohere-python fork.

Verification (tests/test_optional_auth.py, header inspection only, no live calls): empty key omits the header on sync/async v1/v2 and for api_key=lambda: ""; api_key="n/a" still yields Bearer n/a. pytest tests/test_optional_auth.py tests/test_client_init.py → 4 passed, 1 skipped (boto3); mypy src/cohere/overrides.py clean. Reverting the empty-token check fails exactly the 2 relevant tests.

Link to Devin session: https://app.devin.ai/sessions/56fc23472ad04e0cbadf0e7f45d0893b

[devin-ai-integration]

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