fix(tests): mock prisma.Prisma in backoff retry tests to avoid 'prisma generate'

PrismaClient.__init__ does `from prisma import Prisma` inline, which raises
RuntimeError when the Prisma client hasn't been generated.  This caused two
tests to fail in CI with:

  Exception: Unable to find Prisma binaries. Please run 'prisma generate' first.

Add an autouse fixture that replaces sys.modules['prisma'] with a MagicMock
for the duration of each test, allowing PrismaClient to be instantiated and
client.db to be overridden with the existing mock objects.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/proxy_unit_tests/test_prisma_client_backoff_retry.py

@@ -22,6 +22,20 @@ import httpx
 import backoff
 
 
+@pytest.fixture(autouse=True)
+def mock_prisma_binary():
+    """Mock prisma.Prisma to avoid requiring 'prisma generate' in CI.
+
+    PrismaClient.__init__ does `from prisma import Prisma` inline, which raises
+    RuntimeError when the Prisma client hasn't been generated yet.  Replacing
+    sys.modules['prisma'] with a MagicMock lets the import succeed so tests can
+    instantiate a real PrismaClient and override client.db with their own mocks.
+    """
+    mock_module = MagicMock()
+    with patch.dict(sys.modules, {"prisma": mock_module}):
+        yield
+
+
 @pytest.fixture
 def mock_prisma_client():
     """Create a mock PrismaClient with necessary attributes"""