The adaptive heartbeat tick counter (vm->heartbeat.tick_count) is the
project's sole canonical clock for timing measurements -- host wall-clock
is not a valid substitute. Exposes it read-only so DoE/overhead campaigns
can measure elapsed ticks instead of wall-clock deltas.
Verified: three-arch QEMU acceptance (amd64/aarch64/riscv64), POST
1012/0/0 on each, HEARTBEAT-TICKS@ live-tested returning a real non-zero
count on all three.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
