build: treat warnings as errors (#464)

* build: treat warnings as errors

* silence warning from googleapis-common-protos

Author: parthea

pytest.ini

@@ -0,0 +1,13 @@
+[pytest]
+filterwarnings =
+    # treat all warnings as errors
+    error
+    # Remove once https://github.com/protocolbuffers/protobuf/issues/12186 is fixed
+    ignore:.*custom tp_new.*in Python 3.14:DeprecationWarning
+    # Remove once https://github.com/grpc/grpc/issues/35086 is fixed
+    ignore:There is no current event loop:DeprecationWarning:grpc.aio._channel
+    # Remove once release PR https://github.com/googleapis/proto-plus-python/pull/391 is merged
+    ignore:datetime.datetime.utcfromtimestamp\(\) is deprecated:DeprecationWarning:proto.datetime_helpers
+    # Remove once https://github.com/googleapis/python-api-common-protos/pull/187/files is merged
+    ignore:.*pkg_resources.declare_namespace:DeprecationWarning
+    ignore:.*pkg_resources is deprecated as an API:DeprecationWarning