chore(CI): add CI jobs for package dependency specification and lower bounds

[Sudha247]

Fixes #13731.

This is to catch any packaging errors early. This tries to replicate the opam-repo-ci job, which does this (one instance here: https://opam.ci.ocaml.org/github/ocaml/opam-repository/commit/a95df9014bc79103fde668cf2adbe6680fd2f9cf/variant/compilers,5.0,fs-io.3.21.0~alpha3,tests), but within source.

The opam-repo-ci job clones the whole opam-repository and adds the PR as its overlay and tries to install a particular package. We do something similar here by installing dependencies of a specific package and building only that package. I tried to do it without pinning other packages within Dune, but that proved to be tricky; Most packages in the dev repo require the development version of Dune and sibling packages (where there are dependencies on sibling packages). So, I resorted to only pinning the packages and not installing them, thus making them available to the solver, but the packages themselves don't influence the solver.

Note: This matrix creates an independent job for every package. I haven't yet figured out how to make it less noisy in GitHub Actions.

[Sudha247]

There's a failing job for dune.opam

/home/runner/work/dune/dune/_opam/bin:/opt/hostedtoolcache/opam/2.5.0/x86_64:/snap/bin:/home/runner/.local/bin:/opt/pipx_bin:/home/runner/.cargo/bin:/home/runner/.config/composer/vendor/bin:/usr/local/.ghcup/bin:/home/runner/.dotnet/tools:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
File "bin/dune", line 48, characters 2-4:
48 |   re)
       ^^
Error: Library "re" not found.
-> required by _build/default/bin/main.exe
-> required by _build/install/default/bin/dune
-> required by _build/default/dune.install
-> required by alias install

I suspect because dune.opam doesn't specify this as dependency.

[shonfeder]

Looking good! I'm very happy to see the actions passing :D Have you been able to test that it can identify packaging errors? (E.g., perhaps by reversing the csexp lower bound added in https://github.com/ocaml/dune/pull/13730/changes ?)

[Sudha247]

Here's reversing #13730 in a test branch and it reproduces the lower bounds failure: https://github.com/Sudha247/dune/actions/runs/23433560103/job/68165835580?pr=3

[Sudha247]

I'm not sure the Windows CI failure is related - this PR is not touching any related code.

[shonfeder]

LGTM!

We can use this on the pending patch release. Thanks! :)