chrono-machines vs shipper-retry vs mailrs-backoff

Exponential, constant, and Fibonacci backoff retry library with full jitter support - no_std compatible

Retry strategies and backoff policies for shipper

Exponential backoff with optional jitter (AWS-style taxonomy: None / Equal / Full). Pure delay math — no I/O, no async, no allocation. Useful for any retry loop: SMTP outbound, webhook delivery, auth-lockout, HTTP client retries.