Pods 2.5 optimizations work

This is a general PR for all the 2.x-optimizations work done so far by @jamesgol / @pglewis; to ensure we can see a full big picture of the changes. This will make it easier to review everything as it currently is (or becomes) and I can comment on the difference lines.
I'm not sure whether our actions for the Pods class were named pods_pods_* or pods_*, I'm pretty sure we originally settled on pods_pods_* to avoid issues with general / global filters and actions named pods_*. So naming them pods_* like here and other places will produce backwards compatibility issues, introducing breaking changes.