DSN retryability ignores additional recipient delivery statuses #1681

Problem

The delivery-status retryability check only examines one recipient status. A multi-recipient DSN can therefore be classified from the first status while later recipients contain temporary or permanent failures that change the correct result.

Prepared commit f4b0ea10b75631846b9db573700de8e540df7cba evaluates every recipient delivery status and preserves existing single-status behavior.

External models cover mixed success, transient and permanent status sequences. The unchanged 1,837-example suite passes on Ruby 4.0.6 and 3.2.11, with package and Action Mailer integration green.

CONTRIBUTING requires regression specs, so this report does not open a source-only PR or modify tests.