chore: Update vertex ai in example store and rag retrieval to use proxy

PiperOrigin-RevId: 825237803

src/google/adk/dependencies/vertexai.py

@@ -15,4 +15,5 @@
 from __future__ import annotations
 
 import vertexai
+from vertexai.preview import example_stores
 from vertexai.preview import rag

src/google/adk/examples/vertex_ai_example_store.py

@@ -12,10 +12,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from __future__ import annotations
+
 from google.genai import types
 from typing_extensions import override
-from vertexai.preview import example_stores
 
+from ..dependencies.vertexai import example_stores
 from .base_example_provider import BaseExampleProvider
 from .example import Example
 

src/google/adk/tools/retrieval/vertex_ai_rag_retrieval.py

@@ -22,8 +22,8 @@ from typing import TYPE_CHECKING
 
 from google.genai import types
 from typing_extensions import override
-from vertexai.preview import rag
 
+from ...dependencies.vertexai import rag
 from ...utils.model_name_utils import is_gemini_2_or_above
 from ..tool_context import ToolContext
 from .base_retrieval_tool import BaseRetrievalTool