v1.2.0

Four additions across the channel registry, SMS, and diagnostics.

• Channel registry methods extracted into a dedicated RegistersChannels trait; via() and __call() remain in BaseNotification for discoverability
• BaseNotification::flushChannelRegistry() resets the global channel registry — call it in setUp/tearDown to isolate tests
• SmsMessage gains sender ID support via from() and getFrom(), giving drivers access to the from-number or sender ID without hardcoding it
• FcmChannel and SmsChannel now throw a descriptive RuntimeException when no driver is bound, instead of a generic container resolution error