chore: GenAI SDK client - fix mypy errors in client.py

PiperOrigin-RevId: 832340202

Author: sararob

vertexai/_genai/client.py

@@ -289,7 +289,7 @@ def _get_api_client(
             )
 
     @property
-    def agent_engines(self):
+    def agent_engines(self) -> "'agent_engines.AgentEngines'":
         if self._agent_engines is None:
             try:
                 # We need to lazy load the agent_engines module to handle the
@@ -307,7 +307,7 @@ def agent_engines(self):
         return self._agent_engines.AgentEngines(self._api_client)
 
     @property
-    def prompts(self):
+    def prompts(self) -> "'prompts.Prompts'":
         if self._prompts is None:
             # Lazy loading the prompts module
             self._prompts = importlib.import_module(
@@ -321,7 +321,7 @@ def prompts(self):
         "The Vertex SDK GenAI datasets module is experimental, "
         "and may change in future versions."
     )
-    def datasets(self):
+    def datasets(self) -> "'datasets.Datasets'":
         if self._datasets is None:
             self._datasets = importlib.import_module(
                 ".datasets",