Fix voice-ref denoise crash when mamba_ssm is missing

The existing try/except only wrapped REUSEUpsampler construction, but the
mamba_ssm import is deferred to _lazy_load() which fires from __call__.
So construction silently succeeded, the session sentinel was never set,
and the first generate request blew up with ModuleNotFoundError.

Wrap the __call__ site too. Trip the sentinel and return the original
voice unmodified - same fallback semantics as the construction failure.

src/inference_server.py

@@ -292,7 +292,16 @@ class TTSServer:
         mono = mono.contiguous()
 
         t0 = time.time()
-        cleaned, _ = self._ref_denoiser(mono, in_sr=int(voice.sampling_rate))
+        try:
+            cleaned, _ = self._ref_denoiser(mono, in_sr=int(voice.sampling_rate))
+        except (ImportError, ModuleNotFoundError, RuntimeError) as e:
+            # Lazy-load inside __call__ can still raise on missing mamba_ssm /
+            # selective_scan_cuda kernels even though construction succeeded
+            # (REUSEUpsampler defers the import to first call). Trip the
+            # session-wide sentinel so subsequent calls skip cheaply.
+            logging.warning(f"Voice-ref denoise disabled mid-call (RE-USE unavailable: {e})")
+            self._ref_denoiser = False
+            return voice
         if cleaned.dim() == 2 and cleaned.shape[0] == 1:
             cleaned = cleaned[0]
         # Restore the (1, C=1, T) shape that the rest of the pipeline expects