Do not transform search space in-place in Modelbridge._get_transforme…

…d_gen_args (#2386)

Summary:
Pull Request resolved: #2386

The current setup leads to issues when calling `evaluate_acquisition_function()` in between generation steps, see discussion on #2083

Reviewed By: saitcakmak

Differential Revision: D56400492

ax/modelbridge/base.py

@@ -690,6 +690,7 @@ def _get_transformed_gen_args(
  # TODO(T34225037): replace deepcopy with native clone() in Ax
  pending_observations = deepcopy(pending_observations)
  fixed_features = deepcopy(fixed_features)
+ search_space = search_space.clone()
 
  # Transform
  for t in self.transforms.values():