chore: lazy import yaml in types.py

PiperOrigin-RevId: 831577224

Author: google-genai-bot

google/genai/types.py

@@ -86,11 +86,6 @@
 
 if typing.TYPE_CHECKING:
   import yaml
-else:
-  try:
-    import yaml
-  except ImportError:
-    yaml = None
 
 _is_httpx_imported = False
 if typing.TYPE_CHECKING:
@@ -10298,7 +10293,9 @@ def to_yaml_file(self, file_path: str, version: Optional[str] = None) -> None:
     Raises:
         ImportError: If the pyyaml library is not installed.
     """
-    if yaml is None:
+    try:
+      import yaml
+    except ImportError:
       raise ImportError(
           'YAML serialization requires the pyyaml library. Please install'
           " it using 'pip install google-cloud-aiplatform[evaluation]'."