- Enhanced the `mailer` provider to support email attachments, including both regular and inline attachments.
- Updated the `buildMessage` method to handle multipart email formats for messages with attachments.
- Added new tests for attachment handling in `mailer_test.go` and `mailgun_test.go`, ensuring comprehensive coverage for single, multiple, and inline attachments.
- Revised `TODO.md` to reflect the completion of attachment support across email providers, confirming that all major providers now support this feature.
- Modified the test for scheduled email delivery to assert that the delivery time includes a timezone offset in the RFC1123Z format.
- Replaced the previous check for "GMT" with a regex assertion to ensure compliance with the expected format.
- Enhanced GitHub Actions workflows by refining Mailgun, SMTP, and Twilio configurations for better unit and PR testing.
- Streamlined environment variable management for email and SMS services, ensuring consistent and secure credential handling.
- Updated related tests to validate the new configuration setup, improving overall reliability in communication functionalities.
