Add support for OCaml 5.00

[kit-ty-kate]

Simplified version of #5 for easy review of the significant changes: Obj.set_tag is currently used in cubicle and I believe the new API introduced in #5 by @shakthimaan is here to workaround that.

In this PR I’ve simply commented out this part with a comment specifying why as it should be still correct, only just a bit slower (the use of Obj.set_tag is only here for performance improvement if I understand correctly)

[shakthimaan]

Thanks for the simplified version. Is this PR ready to be merged?

[gasche]

@conchon, @alexandrina-k: are you interested in PRs to add OCaml 5 support? Cubicle currently shows in the list of projects broken by OCaml 5, and @shakthimaan, @kit-ty-kate, @lthls and myself all spent some time trying to help you upgrade the codebase, but so far you have not merged anything -- it's been 8 months now. The OCaml 5 release is going to happen soon; if you don't have time to look at this, it is fine, just say so, we can mark Cubicle incompatible and be done with it.

[ddeclerck]

Hi,
I reached out @conchon about this PR ; we're going to merge it.
Thanks !

[kit-ty-kate]

Is there a release planned? I can do the release on opam-repository if that helps but I'd need a tag to hold on to.

[ddeclerck]

That would help, thanks !
I've just pushed a 1.2.0 release for this purpose.
The minimal OCaml version requirement for this release is now >= 4.08.

[kit-ty-kate]

Thanks. Done here ocaml/opam-repository#22425