Reduce allocations in opamVersionCompare

[talex5]

Test-case:

let ()
  let x0 = Gc.stat () in
  assert (OpamVersionCompare.compare "1.2.3" "1.02.3" == 0);
  let x1 = Gc.stat () in
  Printf.printf "minor_words: %.0f\n" (x1.minor_words -. x0.minor_words)

Before: minor_words: 156
After: minor_words: 84

This just passes all the parameters to loop rather than getting them from the context. Then loop itself isn't needed.

Ideally, there would be no allocations at all. However, removing the others makes the code quite messy so I just did the easy change here.

See https://roscidus.com/blog/blog/2024/07/22/performance-2/#statmemprof for some real-world profiling of the CI solver service, showing this to be a problem.

[kit-ty-kate]

Thanks a lot for this contribution. Would you be able to rebase it on top of #5518 ? I believe with both it should be able to reduce allocation further

[kit-ty-kate]

Our automated benchmark shows a 18% performance improvement. lgtm

[talex5]

I've pushed a commit just to test it on top of #5518. Will need squashing if we decide to keep it.

[kit-ty-kate]

With both work it improves performance by 41%! 🎉

[kit-ty-kate]

I've put back the previous state and will merge this as soon as CI finishes, i'll update my PR on top of master after. Thanks again!