Bump to (OCaml4.14 + Core.v0.16) / (OCaml5.2 + Core.v0.17)

[glyh]

This is part of the bigger plan bumping Mina to OCaml 5.2.1 with Corev0.17.1

[glyh]

These are auto format

[dannywillems]

FWIW: OCaml 5.2.x is already 2 years old, see https://ocaml.org/releases. OCaml 5.5.0 brings a set of interesting features, and there have been other improvements since 5.2.x.

[glyh]

We're bumping up step by step. But I'd love to bump to 5.5.0 if there's no obvious blockers as well -- it just need to be investigated.

Thanks for the recommendation @dannywillems :)

[dkijania]

@glyh question if existing tests are enough to cover this bump?

[glyh]

@dkijania Good question — I went through the full diff to answer it. I believe the existing tests are sufficient for this bump, for two reasons:

1. The changes are mechanical, not semantic. The ~430 changed lines fall entirely into these buckets:

• Core_kernel → Core renames (Core v0.17 merged Core_kernel into Core) and Caml.* → Stdlib.*;
• Sys.getenv_opt → Core's Sys.getenv (same string option semantics) and Sys.getcwd → Sys_unix.getcwd;
• ocamlformat 0.28 reformatting (functor argument indentation etc.);
• dune/opam constraint bumps, CI and Dockerfile updates.

There are no algorithmic or data-structure changes, so what needs coverage is "does everything still compile and behave the same", not new logic.

2. What the suite exercises is the right regression surface for this kind of change. dune runtest runs: the src/tests Alcotest suite (Checked/Typ/As_prover machinery over the pure-OCaml test backend + the Fermat example), inline let%tests across snark0, utils, sponge, group_map and snarkette/fields, the fold_lib/interval_union suites, and the sponge Poseidon test vectors — the last one being a good end-to-end check that the Core bump didn't perturb hashing.

Two caveats, one of which is now addressed:

• CI originally only built 5.2.1 after this PR, while the opam constraints still accept Core v0.16. I've added a symmetric CI matrix (c76de53) that pins the toolchain pairs explicitly — OCaml 5.2.1 + core.v0.17.2 and OCaml 4.14.2 + core.v0.16.2 — so both supported combinations are built and tested on every PR.
• The ultimate acceptance test is building Mina against this branch, since snarky's own tests run on a dummy backend rather than the real Kimchi integration. That part is outside this repo's suite.