fix(bigtable): correct get_bigtable_data_client return annotation

The return annotation referenced bigtable.BigtableDataClient, but that
name is not exported from the google.cloud.bigtable top-level namespace
(only Client is). The client is constructed from google.cloud.bigtable.data,
which is where BigtableDataClient actually lives and is already imported.

Because of "from __future__ import annotations" the annotation is a lazy
string, so it does not fail at runtime, but typing.get_type_hints() and doc
tooling raise AttributeError when resolving it. Point the annotation at
data.BigtableDataClient (the type actually returned) and add a regression
test that get_type_hints() resolves it.

Author: anxkhn

src/google/adk/tools/bigtable/client.py

@@ -31,7 +31,7 @@ def _get_client_info() -> google.api_core.client_info.ClientInfo:
 
 def get_bigtable_data_client(
     *, project: str, credentials: Credentials
-) -> bigtable.BigtableDataClient:
+) -> data.BigtableDataClient:
   """Get a Bigtable client."""
 
   bigtable_data_client = data.BigtableDataClient(

tests/unittests/tools/bigtable/test_client.py

@@ -12,10 +12,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import typing
 from unittest import mock
 
 from google.adk.tools.bigtable import client
 from google.auth.credentials import Credentials
+from google.cloud.bigtable import data
 
 
 def test_get_bigtable_data_client():
@@ -48,3 +50,9 @@ def test_get_bigtable_admin_client():
         credentials=mock_creds,
         client_info=mock.ANY,
     )
+
+
+def test_get_bigtable_data_client_return_annotation_resolves():
+  """The data client return annotation must resolve to a real type."""
+  hints = typing.get_type_hints(client.get_bigtable_data_client)
+  assert hints["return"] is data.BigtableDataClient