fix: prevent task output loss when mixing sync and async tasks

[Rakshit-gen]

Fixes #4137

When processing async tasks, _process_async_tasks returns a new list containing only async task outputs. The caller was replacing the existing task_outputs list instead of extending it, causing all previous sync task outputs to be silently lost.

Changed assignment (=) to extend() at all affected locations:

• _execute_tasks() lines 1155, 1169
• _aexecute_tasks() lines 960, 976
• _handle_conditional_task() line 1182
• _ahandle_conditional_task() line 990

This ensures sync task outputs accumulated before async tasks are preserved when async tasks are collected.

---

Note

Replaces overwriting of task_outputs with extend() when resolving async tasks to prevent loss of prior sync outputs in both sync and async execution paths, including conditional handlers.

• Execution flow (crew.py)
  • Replace task_outputs = ..._process_async_tasks(...) with task_outputs.extend(...) in:
    • *_aexecute_tasks() and *_execute_tasks() when flushing pending async tasks mid-loop and at the end.
    • *_ahandle_conditional_task() and *_handle_conditional_task() before conditional evaluations.
  • Ensures previously accumulated sync outputs are preserved when mixing async and sync tasks and during conditional task handling.

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[Rakshit-gen]

@gabemilani can we look into these changes?