chore: add tracing context note for parallel executor submissions

Agent-Logs-Url: https://github.com/MervinPraison/PraisonAI/sessions/67d22169-f2e6-4727-9804-065fd54f9f78

Co-authored-by: MervinPraison <454862+MervinPraison@users.noreply.github.com>

Author: Copilot

src/praisonai-agents/praisonaiagents/tools/call_executor.py

@@ -167,6 +167,7 @@ def _execute_single_tool(tool_call: ToolCall) -> ToolResult:
         with concurrent.futures.ThreadPoolExecutor(max_workers=self.max_workers) as executor:
             # Submit all tool calls
             future_to_index = {
+                # Preserve contextvars (tracing/session context) across worker threads.
                 executor.submit(copy_context_to_callable(_execute_single_tool), tool_call): i
                 for i, tool_call in enumerate(tool_calls)
             }