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.
Should we be storing this into `self::$table_info_cache[ $transient ]` if `$_info` is not empty?