v0.9.1: Memory leak fix for task system

What's Changed

Added

• vm_task_cleanup(): New API to cleanup task system and free allocated task stacks
  • Should be called before vm_destroy() to prevent memory leaks
  • Frees all task stacks (ds_base, rs_base) allocated by vm_task_spawn()
  • Resets scheduler and message queue state

Fixed

• Memory leak in task system detected by AddressSanitizer
  • Task stacks allocated by vm_task_spawn() were not being freed
  • All test cases now properly call vm_task_cleanup() before vm_destroy()

Full Changelog: v0.9.0...v0.9.1

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