Add :with-test to test dependencies

[Julow]

In the dune-project file, alcotest was declared as a normal dependency.
Also used the same logic when generating the opam file.

[Julow]

There's no diffs in an opam file so I thought this meant success but actually the deps should have been reordered. There's no opam file generated in the examples !

[Julow]

There's a problem with the formatter. (this is from the first commit)