cache multiple rsp in one test fn, switch cache to global use

tests/metagpt/provider/conftest.py

@@ -0,0 +1,8 @@
+import pytest
+
+
+@pytest.fixture(autouse=True)
+def llm_mock(rsp_cache, mocker, request):
+    # An empty fixture to overwrite the global llm_mock fixture
+    # because in provider folder, we want to test the aask and aask functions for the specific models
+    pass