Function thread_init_hook_for_tuning 

pub fn thread_init_hook_for_tuning(
    pinning: PinningPreset,
    sched: SchedPreset,
) -> Result<Option<ThreadInitHook>, String>

Build a per-thread init hook that applies tuning to executor threads.

• Pinning is best-effort: failures warn and continue.
• Scheduler changes are enforced when requested: failures return an error.