fix: SimulationAgent.inventory reads only from agent's own position (#4239)

The inventory property was iterating through ALL observation tokens
(including other agents' inventories) instead of only looking at
tokens at the center position where the agent sees itself.

Author: daveey

packages/mettagrid/python/src/mettagrid/simulator/simulator.py

@@ -377,7 +377,14 @@ def inventory(self) -> Dict[str, int]:
         inv = {}
         obs = self.observation
 
+        # Agent's own tokens are at the center of the observation window
+        c_sim = self._sim._c_sim
+        center = (c_sim.obs_height // 2, c_sim.obs_width // 2)
+
         for token in obs.tokens:
+            # Only look at tokens at the agent's own position (center)
+            if token.location != center:
+                continue
             # Check if this is an inventory feature
             if token.feature.name.startswith("inv:"):
                 # Extract resource name from "inv:resource_name" format