nx_perf_counters_test.nx

nx_perf_counters_test.nx -- validate the bits-up perf-counter reader in pure NishiLang: open a hardware INSTRUCTIONS counter, run a known workload, read the delta. A positive count proves we can measure real CPU activity DIRECTLY from the silicon's PMU -- the STATE-INDEPENDENT energy foundation (works charging, on AC, on a battery-less server) -- with no libc, no `perf`, no C. Known answer: instruction delta > 0 (and within a sane band of the work done) -> exit 0. If perf_event_open is unavailable (locked-down kernel), it reports the errno and exits non-zero loudly -- never silently faking a number.