OCaml 5+ is a multicore release

[dra27]

Partial fix (hopefully) for the problems being seen with lwt, etc.

[dra27]

This is deployed on live at the moment, and has unblocked, say, Lwt. See also ocurrent/ocaml-version#58.

[dra27]

Now that OCaml 5 is multicore, it's possible that a lot of this special-case trickery used for multicore isn't necessary. However, it's important if that's implemented to be sure that we don't lose the testing matrix... e.g. for Lwt, the main libraries should continue to be tested on 4.08-5.0 with lwt_domain only being tested on 5.0.

[tmcgilchrist]

This explicit is_multicore code has been removed and should be handled correctly in solver-service / ocaml-ci. I've added a test in #73 to be more explicit about it.

It might also be useful to have some testing in ocaml-ci to ensure certain packages have stable Analysis results. LWT project being a good example which should have a solution for many older OCaml versions.