feat: simplify stage configuration logic in AsstProxy

Remove redundant condition for setting stage in Fight type tasks. Now always set the stage from the main parameter, and only override with standby_stage for subsequent iterations when standby_stage is provided. This makes the logic more straightforward and reduces unnecessary branching.

Author: EvATive7

src/model.py

@@ -247,9 +247,8 @@ def run_maatask(self, maatask, time_remain) -> "MaataskRunResult":
 
             try:
                 if type == "Fight":
-                    if i == 0:
-                        config["stage"] = stage
-                    else:
+                    config["stage"] = stage
+                    if i != 0 and standby_stage:
                         config["stage"] = standby_stage
 
                 self.add_maatask(type, config)