Defines a GenericNotifier trait and Notification struct that standardizes how alerts are dispatched across multiple channels. The trait requires implementors to define `attempt`, `can_notify`, and `name` methods, and provides retry logic with exponential backoff. This pattern is reusable for any system that needs to send notifications through multiple providers with consistent retry and escalation semantics.

Implements a ReplicaURL enum that parses custom URL schemes (icmp, tcp, ssh, http, https) into typed variants. The `parse_from` method handles IPv6 address formatting correctly. This is a clean, self-contained URL parser that could be extracted for any project needing to parse non-standard URI schemes.

Reads TOML configuration files and substitutes environment variables using the `envsubst` crate. Includes validation of duplicate identifiers across services and nodes. This pattern is reusable for any Rust application that needs to load configuration with environment variable interpolation and structural validation.