perf(zerogpu): cap generate_image GPU slot at duration=45 for better scheduling

app.py

@@ -975,7 +975,7 @@ def _anima_step_progress(pipe, callback, total_steps):
         sched.step = orig
 
 
-@spaces.GPU
+@spaces.GPU(duration=45)
 def generate_image(
     model_name,
     prompt,