Exercises the slot-scan logic in event_log_init(): after a simulated
reboot (RAM state cleared, NVS slots preserved) the module must
resume with the correct head/cnt so newest-first read order is
unchanged and subsequent writes continue the seq monotonically.
Adds native-only event_log_test_simulate_reboot() helper. Lifts the
slot-scan loop out of the #ifdef ARDUINO guard so the native stub
exercises the same recovery path as production; the platform-specific
NVS setup remains guarded.