Constant it waits for a fixed period of time between calls.

Exponential it waits for "delta * e^attempts" time between calls.

Exponential2 it waits for "delta * 2^attempts" time between calls.

Fibonacci it waits for "delta * fibonacci(attempt)" time between calls.

JitterUp adds random jitter to the interval.

Linear it waits for "delta * attempt" time between calls.

Zero it waits for zero time between calls.

BackoffFunc denotes a family of functions that control the backoff duration between call retries.