The Best Way to always load the newest version of 3rd party code

Short version — there isn’t one. WordPress doesn’t handle dependencies logic in any form. If library itself doesn’t include any mechanism for it (which is exceedingly rare) — there isn’t anything you can do.

At best you can (and should) check if expected version of dependency is loaded (if it exposes version in some form or at least by location it’s loaded from).

In private sites this can be handled (via Composer for example), but there is no good solution for publicly distributed code.