v0.9.0 of coffrify

Official Dart SDK for Coffrify, encrypted file transfer infrastructure: transfers, webhooks, API keys, audit, vaults and 30+ resources. Pure Dart, no Flutter dependency. Changelog excerpt: - Initial public release of the Coffrify Dart SDK (pure Dart core). - Transfers, webhooks (Standard Webhooks), API keys, audit, vaults and 30+ resources. - Retry policies, circuit breaker, rate limiter, idempotency stores, request hooks, telemetry adapter.