Function yield_cpu_local 

pub(super) fn yield_cpu_local(
    cpu: &mut SchedulerCpu,
    cpu_index: usize,
) -> Option<SwitchTarget>

Prepare a LOCAL-only context switch.

Updates the TSS, SYSCALL RSP, and CR3 for the next task. Returns the raw pointer pair needed by do_switch_context.

Returns None if there is no task to switch to (same task or invalid context).