fix(video_gen): parse duration suffix in success_response

int(payload["duration"]) blows up on "4s" (veo3.1 format).
Strip non-digit chars before int conversion in the response builder.

plugins/video_gen/fal/__init__.py

@@ -597,7 +597,7 @@ class FALVideoGenProvider(VideoGenProvider):
             prompt=prompt,
             modality=modality_used,
             aspect_ratio=aspect_ratio if "aspect_ratio" in payload else "",
-            duration=int(payload["duration"]) if "duration" in payload else 0,
+            duration=int("".join(c for c in payload["duration"] if c.isdigit()) or "0") if "duration" in payload else 0,
             provider="fal",
             extra=extra,
         )