fix memory leak

vms/services/monitoring.py

@@ -223,6 +223,7 @@ class MonitoringService:
         Returns:
             Matplotlib figure with CPU usage plot
         """
+        plt.close('all')  # Close all existing figures
         fig, ax = plt.subplots(figsize=(10, 5))
         
         if not self.timestamps:
@@ -268,6 +269,7 @@ class MonitoringService:
         Returns:
             Matplotlib figure with memory usage plot
         """
+        plt.close('all')  # Close all existing figures
         fig, ax = plt.subplots(figsize=(10, 5))
         
         if not self.timestamps:
@@ -312,6 +314,7 @@ class MonitoringService:
         num_cores = len(self.cpu_cores_percent)
         if num_cores == 0:
             # No data yet
+            plt.close('all')  # Close all existing figures
             fig, ax = plt.subplots(figsize=(10, 5))
             ax.set_title("No per-core CPU data available yet")
             return fig