oUnit2 support

[RiderALT]

oUnit now is ounit2.

https://github.com/gildor478/ounit#transition-to-ounit2

Also, qtest is not compatibility with ounit2 at least in this case:
the test function now takes test_ctxt argument, so replace all fun () -> ...) by fun test_ctxt -> ...
i
all compatibility issues is reproduced during build ocaml gen and ocaml iter packages from opam.

[c-cube]

note that ounit2 still provides a OUnit module, to the best of my knowledge. So the current code still works if you use OUnit?

[c-cube]

I think it should be possible to generate code for OUnit or OUnit2 depending on a flag.

[RiderALT]

No.
dune totally ignore qcheck transition package.
$ dune installed-libraries |grep qcheck
qcheck-alcotest (version: 0.13)
qcheck-core (version: 0.13)
qcheck-core.runner (version: 0.13)

META file in qcheck is empty:
$ wc -l /usr/lib64/ocaml/qcheck/META
1 /usr/lib64/ocaml/qcheck/META

qcheck was builded by dune-2.3.0

I think that the error is somewhere in the qcheck build or in process process of generation META in a dune-2.3.0.

but porting qtest to oUnit2 would definitely help me.