ocaml-sdls: fix security_eio.mli example to compile with MDX
The example used 'fs', '...' and shorthand module references that don't
type-check. Wrap it in a 'run ()' function that takes env from
Eio_main.run, qualify Sdls_eio.Security_eio / Sdls.Security /
Sdls.Mc.Bad_mac fully, and replace the trailing '...' with a real
Printf.printf so the build catches drift.