Compute the ISO timestamp after which the next probe is due.
The delay doubles with each attempt (exponential back-off), capped at MAX_BACKOFF_MS:
ISO timestamp used as the reference point (lastProbedAt)
Total probe attempts recorded so far (≥ 1)
ISO timestamp after which the next probe should be issued
Compute the ISO timestamp after which the next probe is due.
The delay doubles with each attempt (exponential back-off), capped at MAX_BACKOFF_MS: