Fix use of ocaml re package

[franziskuskiefer]

The ocaml re package is used for error messages. But it seems to be crashing when using ocaml 4 on some machines.

• [x] Assess if the packages is really needed or if hax could do without.
• [ ] If it is really needed, assess the issues with ocaml 4 and either fix them or require ocaml 5 for hax.

[W95Psp]

re is used to link our printed Rust to pretty printed rustfmt Rust, this pretty printing can be disabled with HAX_RUSTFMT=no.

We need to use the new generic printer to write a Rust printer (see https://github.com/hacspec/hax/issues/1110), and then we can stop using rustfmt within the engine.

[W95Psp]

Quoting @franziskuskiefer: "running it on some of the Rust crypto crates like sha2 or hmac will run into that issue"

Let's investigate when we have time, we should have a reproducer here. It makes no sense that re behavior changes between OCaml 4 and OCaml 5.

[github-actions[bot]]

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[W95Psp]

Since https://github.com/cryspen/hax/pull/694, we are using OCaml 5, so the issue should not reproduce on main.