Split OPAM packages
This should make CI failures faster by compiling most of Prosa (the coq-prosa OPAM package) before compiling the dependencies (CoqEAL) and the remaining (coq-prosa-refinements package).
This should make CI failures faster by compiling most of Prosa (the coq-prosa OPAM package) before compiling the dependencies (CoqEAL) and the remaining (coq-prosa-refinements package).