Use new `handleLoad` hook when released and available

[Lms24]

Something to follow up on which hasn't yet landed - handle(Server)Load hooks: sveltejs/kit#11313

My first take: When this lands, we export handlers for it from our SDK but continue with auto instrumentation. In v9 we drop 1.x support, remove auto instrumentation and switch to exclusively instrumenting load functions via handle(Server)Load. If we adjust the wizard to add the handlers automatically at this point, I believe we should be good.