Hmedina patch 2

[hmedina]

Fix #650 by explicitly stating the unix library imports. Most ka-things import kappa_generic_toolset, and so adding unix to that library's Dune stanza solved most of the warnings. The version object got a command-line flag instead.

Changes to the continuous integration script are just to strengthen it against a known failure mode, as documented in that commit message (https://github.com/Kappa-Dev/KappaTools/commit/d796fa7e39c918bd4a6dc881d0c2b6efb7ef0ccd)

Although the KappaTools compile under OCaml 5, the documentation appears to require tyxml, which does not yet support OCaml 5 (see https://github.com/Kappa-Dev/KappaTools/commit/b9fe862fea9718eada0edb2810328cc63ddacfcf), and so OCaml 5 can't be included in the build matrix (yet...)