Fix UnboundLocalError: move torch._dynamo import to module level

import inside a function creates a local binding that shadows the
module-level torch import, breaking all earlier torch references in
the same function scope.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

engine.py

@@ -1,6 +1,7 @@
 import logging
 import time
 import torch
+import torch._dynamo
 from typing import Optional, Tuple
 
 logger = logging.getLogger(__name__)
@@ -52,7 +53,6 @@ def load_model() -> bool:
             # s3gen (HiFiGAN vocoder + flow matching) since that's the bottleneck.
             # suppress_errors=True falls back to eager for any op compile can't handle.
             try:
-                import torch._dynamo
                 torch._dynamo.config.suppress_errors = True
                 chatterbox_model.s3gen = torch.compile(chatterbox_model.s3gen, dynamic=True)
                 logger.info("s3gen compiled with torch.compile")