fix: make TelemetryCollector.stop() consistent with shutdown behavior

Ensures TelemetryCollector.stop() calls shutdown() instead of just flush()
for consistency with the main atexit handler and proper PostHog session cleanup.

Co-authored-by: Mervin Praison <MervinPraison@users.noreply.github.com>

Author: github-actions[bot]

src/praisonai-agents/praisonaiagents/telemetry/telemetry.py

@@ -354,8 +354,8 @@ def start(self):
         pass
 
     def stop(self):
-        """Stop telemetry collection and flush data."""
-        self.telemetry.flush()
+        """Stop telemetry collection and properly shutdown."""
+        self.telemetry.shutdown()
 
     def trace_agent_execution(self, agent_name: str, **attributes):
         """Compatibility method for agent execution tracking."""