fix(E600): enforce test module conventions across packages
- ocaml-sqlite: merge generic_suite into suite, single export in .mli
- ocaml-tcpcl: add missing test_tcpcl.mli
- ocaml-tls: rename test_rng to mock_rng (helper, not test module)
- ocaml-tls: restructure test_tls_eio/unix stubs with test.ml runners
- ocaml-tomlt: restructure test_tomlt_{bytesrw,eio,unix} stubs with
test.ml runners and .mli files