fix: avoid nested progress bars causing LiveError

The `_process_candidates` method had a progress bar context that called
`get_next_candidate()`, which could recursively call `_process_candidates`
again. This created nested progress bars, causing Rich's LiveError:
"Only one live display may be active at once".

Fixed by moving the `get_next_candidate()` call outside the progress bar
context manager.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: misrasaurabh1

codeflash/optimization/function_optimizer.py

@@ -369,7 +369,9 @@ def _process_candidates(
                 logger.info(success_msg.format(len(candidates), self.candidate_len))
 
             callback()
-            return self.get_next_candidate()
+        # Call get_next_candidate() OUTSIDE the progress_bar context to avoid
+        # nested progress bars (Rich only allows one active Live display at a time)
+        return self.get_next_candidate()
 
     def _filter_refined_candidates(self, candidates: list[OptimizedCandidate]) -> list[OptimizedCandidate]:
         """We generate a weighted ranking based on the runtime and diff lines and select the best of valid optimizations to be tested."""