Remove firestore emulator from test dependencies

tests/conftest.py

@@ -2,25 +2,23 @@
 
 from __future__ import annotations
 
-import os
 import uuid
 
 import pytest
 import pytest_asyncio
-from google.cloud.firestore_v1.async_client import AsyncClient
 
 from va_agent.session import FirestoreSessionService
 
-os.environ.setdefault("FIRESTORE_EMULATOR_HOST", "localhost:8602")
+from .fake_firestore import FakeAsyncClient
 
 
 @pytest_asyncio.fixture
 async def db():
-    return AsyncClient(project="test-project")
+    return FakeAsyncClient()
 
 
 @pytest_asyncio.fixture
-async def service(db: AsyncClient):
+async def service(db):
     prefix = f"test_{uuid.uuid4().hex[:8]}"
     return FirestoreSessionService(db=db, collection_prefix=prefix)