fix: cast librosa float64 audio to float32 for Chatterbox voice encoder

The upstream VoiceEncoder's melspectrogram only casts to float32 when
hp.normalized_mels is True (it defaults to False), so librosa's float64
output flows through as double tensors into float32 model weights,
causing 'expected m1 and m2 to have the same dtype, but got: float !=
double'. Fix by monkey-patching prepare_conditionals in both Chatterbox
and Chatterbox Turbo backends to ensure librosa.load returns float32.

backend/backends/chatterbox_backend.py

@@ -178,6 +178,30 @@ class ChatterboxTTSBackend:
                 progress_manager.mark_complete(model_name)
                 task_manager.complete_download(model_name)
 
+            # Monkey-patch prepare_conditionals to cast librosa's float64
+            # audio to float32 before it reaches the voice encoder.  The
+            # upstream VoiceEncoder's melspectrogram only casts to float32
+            # when hp.normalized_mels is True (it defaults to False), so
+            # float64 mels hit float32 model weights → dtype mismatch.
+            _orig_prepare = self.model.prepare_conditionals
+
+            def _f32_prepare(wav_fpath, **kwargs):
+                import librosa as _librosa
+
+                _orig_librosa_load = _librosa.load
+
+                def _load_f32(*a, **kw):
+                    wav, sr = _orig_librosa_load(*a, **kw)
+                    return wav.astype(np.float32), sr
+
+                _librosa.load = _load_f32
+                try:
+                    return _orig_prepare(wav_fpath, **kwargs)
+                finally:
+                    _librosa.load = _orig_librosa_load
+
+            self.model.prepare_conditionals = _f32_prepare
+
             logger.info("Chatterbox Multilingual TTS loaded successfully")
 
         except ImportError as e: