The storage crate had its own RetryConfig struct (max_attempts,
initial_delay, max_delay, backoff_multiplier) duplicating
common::resilience::retry::RetryConfig.
Added backoff_multiplier field to common's RetryConfig and updated
storage to re-export and use common's version with its field names
(max_retries, base_delay). Updated all storage tests accordingly.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>