fix(ltx2): fix missing Optional import in text encoders

Author: Perseus14

src/maxdiffusion/models/ltx2/text_encoders/text_encoders_ltx2.py

@@ -14,7 +14,7 @@
 limitations under the License.
 """
 
-from typing import Tuple, Union, List, Any
+from typing import Tuple, Union, List, Any, Optional
 import jax
 import jax.numpy as jnp
 from flax import nnx