*: declare missing :with-test deps (lint sweep, batch 1)

Add the [(<lib> :with-test)] entries that the new monopam test-scope
lint check flagged as missing -- packages where a [test] stanza
referenced a library but the corresponding opam dep wasn't declared.
Local builds worked because dune sees the union of all deps;
[opam install --with-test] from a fresh switch would fail.

This batch:

- ca-certs add vlog (test/test.ml uses Vlog.setup_test); also
drop the stale [(nox-tls :with-test)] flagged as
unused.
- dupfind add alcotest (test runner).
- monopam add alcotest, astring, merge3 (used in test/).
- monopam-info add alcotest; drop the stale [(fmt :with-test)]
flagged as unused.

Each verified by [dune build] + [dune runtest] before moving on.

Remaining packages with [missing :with-test] reports follow in
subsequent batches; none of them are subtleties, just mechanical
sweeps of the ~40 packages whose tests reference libraries that
weren't declared with the right scope.