Transitional codemod that upgrades adopter code from raw Swoosh.Email
usage to native Mailglass.Message setters.
Use this task as one step in the canonical 0.x -> 1.0 migration path, not
as the whole compatibility contract by itself. The authoritative guide lives
at guides/upgrading-to-v1_0.md.
Options
--apply- actually apply the changes to the files. Default is a dry-run.