*: declare missing :with-test deps (lint sweep, batch 3)
- ocaml-arp add (fmt :with-test)
- ocaml-leb128 add (fmt :with-test)
- ocaml-atproto-handle add (eio_main :with-test)
- ocaml-did add (eio_main :with-test)
- ocaml-monitor add (eio_main :with-test)
Each verified by [dune build] + [dune runtest].