Draft: upgrade caqti

Most SQL function signatures have to be changed in order to use a more recent version of caqti, because of what was done in https://github.com/paurkedal/ocaml-caqti/commit/e22e843d06afada39af8c9422dbfceef0c5f0907

This will be for v9.3 or v9.4.

Also related: https://github.com/paurkedal/ocaml-caqti/commit/5ef1d42b6b4f1c6cb1302bdf57807d5c354918de#commitcomment-50263058

Issue #110 (closed)