Document the safety contracts for:
- acquire_iopl: kernel fd validity, IOPL privilege, no concurrent calls
- inb/inw/inl: valid port, required privilege (IOPL or ring 0)
- outb/outw/outl: valid writable port, no destructive side effects
Closes the documentation gap for io.rs unsafe inline asm blocks.
Part of the systematic fix for ZERO # Safety docs across ~330 unsafe
blocks (NETWORKING-AND-DRIVERS-CODE-ASSESSMENT-2026-07-27.md §9.3).
vasilito
ec8af52952