Accept auth_token in AnthropicFoundry.__init__ so .copy() doesn't crash

[Kymi808]

Summary

Calling .copy() on an AnthropicFoundry (or AsyncAnthropicFoundry) client always raises:

TypeError: AnthropicFoundry.__init__() got an unexpected keyword argument 'auth_token'

The Foundry copy() overload (src/anthropic/lib/foundry.py:204) declares an auth_token parameter and forwards it via super().copy(auth_token=auth_token, ...). The parent Anthropic.copy() (src/anthropic/_client.py:477–479) then unconditionally passes auth_token=auth_token or self.auth_token into self.__class__(...). But AnthropicFoundry.__init__ did not accept an auth_token kwarg, so the call exploded. The async client had the identical bug.

Trivial repro:

from anthropic import AnthropicFoundry
AnthropicFoundry(api_key="…", resource="…").copy()
# TypeError: AnthropicFoundry.__init__() got an unexpected keyword argument 'auth_token'

Fix

Mirror the existing pattern in AnthropicAWS / AsyncAnthropicAWS, which already accept auth_token for exactly this reason (src/anthropic/lib/aws/_client.py:51 — "Passed through to parent but not used for AWS auth"). The implementation __init__ of both AnthropicFoundry and AsyncAnthropicFoundry now accepts auth_token: str | None = None and forwards it to super().__init__(auth_token=auth_token, ...). Foundry's own auth uses an API key / Azure AD token, so the value is plumbing-only — that's why the @overload signatures are left as-is (no public construction option).

Test plan

Added test_copy_does_not_crash to both TestAnthropicFoundry and TestAsyncAnthropicFoundry in tests/lib/test_azure.py. They instantiate a client, call .copy() (and .copy(timeout=...)), and assert the result is a properly typed AnthropicFoundry / AsyncAnthropicFoundry.

• On main: both tests fail with TypeError: ... got an unexpected keyword argument 'auth_token'.
• With this change: pytest tests/lib/test_azure.py → 11 passed.
• ./scripts/lint reports no new errors in the changed files; ruff check and ruff format --check clean.