fix: actually check the endpoint during setup

async_setup_entry handed client.with_options(timeout=10.0).models.list to the
executor. On AsyncOpenAI that returns an awaitable paginator, so it came back
unawaited, no request was made, and a bad key or an unreachable endpoint still
set up. It now awaits client.models.list(timeout=10.0), matching core's
openai_conversation, so a 401 raises ConfigEntryAuthFailed and a connection
error ConfigEntryNotReady, as the README already says.

The shared mock_init_component fixture now patches models.list with an
AsyncMock and keeps the patch for the whole test, because tests that change a
subentry reload the entry and run setup again.

Reported by @MartinNuc in #1.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SUd68TsT5QZ68Dtfw2uWBU

tests/conftest.py

@@ -1,6 +1,6 @@
 """Fixtures for openai_compatible tests."""
 
-from collections.abc import Generator
+from collections.abc import AsyncGenerator, Generator
 from typing import Any
 from unittest.mock import AsyncMock, MagicMock, patch
 
@@ -154,13 +154,19 @@ async def mock_config_entry_with_reasoning_model(
 @pytest.fixture
 async def mock_init_component(
     hass: HomeAssistant, mock_config_entry: MockConfigEntry
-) -> None:
-    """Initialize integration."""
+) -> AsyncGenerator[None]:
+    """Initialize integration.
+
+    The patch stays active for the whole test: setup awaits GET /models, and a
+    test that changes a subentry reloads the entry, which runs setup again.
+    """
     with patch(
         "openai.resources.models.AsyncModels.list",
+        new_callable=AsyncMock,
     ):
         assert await async_setup_component(hass, DOMAIN, {})
         await hass.async_block_till_done()
+        yield
 
 
 @pytest.fixture(autouse=True)