this looks fine to me, feel free to merge when you're ready.

Running the full testsuite locally shows the following unsettling performance behaviour:

OCaml 5.4:

• main (3.1.0): ~2.315s
• misc-improvements: ~2.275s

OCaml 4.14:

• main (3.1.0): ~3.000s
• misc-improvements: ~3.200s

Thanks to a quick godbolt today i learned that (at least for 4.14):

let is_prefix =
  let rec aux ~prefix str =
    ...
  in
  fun ~prefix str -> ...

doesn't seem to create an equivalent native binary to

let is_prefix ~prefix str =
  let rec aux ~prefix str =
    ...
  in
  ...

After splitting #41 away and removing the fun ... -> the new performance numbers are:

OCaml 5.4:

• main (3.1.0): ~2.315s
• misc-improvements: ~2.275s

OCaml 4.14:

• main (3.1.0): ~3.000s
• misc-improvements: ~3.000s