Compute the delay (ms) before the Nth retry, using a 2^N exponential backoff anchored on RETRY_DELAY.
retryCount is the zero-indexed attempt counter (0 = first retry).
retryCount
Compute the delay (ms) before the Nth retry, using a 2^N exponential backoff anchored on RETRY_DELAY.
retryCountis the zero-indexed attempt counter (0 = first retry).