Explain query counts

Fix trivial excesses (2 splits configured & don't fetch courses if there are none)
LMS-11220, LMS-11391, LMS-11390

@doctoryes @cpennington Please review and suggest any other bugs I should enter. what i've put in so far as bugs:
   LMS-11402: split using regex on active_versions and often getting active_versions more than once
   LMS-11403: mongo computing course's inheritance for each item separately on get_items
   LMS-11401: split shouldn't fetch definitions just because it's iterating over fields
   LMS-11400: mongo fetching course directly and via wildcard in get_course
   LMS-11396: split active_versions updated 2x in one query possibly causing race condition?
   LMS-11395: split delete direct only category is not removing it from published only disconnecting it
Maybe do this a fail-fast?

    if not version_guids:
        return []
    
    matching_structures = ...