Function calibrate_apic_timer 

pub fn calibrate_apic_timer() -> u32

Calibrate the APIC timer using PIT channel 2 as a reference.

Uses PIT channel 2 in one-shot mode (~10ms) to measure how many APIC timer ticks elapse. Interrupts should be disabled during calibration.

Returns the number of APIC timer ticks per 10ms, or 0 on failure.