Nothing super fancy here. This just sets config_minNumVisibleRecentTasks to 5000 and config_activeTaskDurationHours to 5000 (over half a year). This should effectively stop android from automatically closing apps.
Xposed/EdExposed/LSPosed required.
Just install the apk, and if you're using LSPosed, enable it for System Framework. Restart and it should work.
Thanks to @JingMatrix for keeping LSPosed alive and to all the previous LSPosed/EdExposed/Xposed devs!