feat: LLMClient protocol with Featherless and mock implementations

tests/test_llm_mock.py

@@ -0,0 +1,21 @@
+import pytest
+from chat.llm.mock import MockLLMClient
+from chat.llm.client import Message
+
+
+@pytest.mark.asyncio
+async def test_mock_returns_canned_response():
+    client = MockLLMClient(canned=["Hello, world."])
+    msgs = [Message(role="user", content="hi")]
+    out = await client.generate(msgs, model="any")
+    assert out == "Hello, world."
+
+
+@pytest.mark.asyncio
+async def test_mock_streams_tokens():
+    client = MockLLMClient(canned=["abcd"])
+    msgs = [Message(role="user", content="hi")]
+    chunks = []
+    async for chunk in client.stream(msgs, model="any"):
+        chunks.append(chunk)
+    assert "".join(chunks) == "abcd"