The InterfaceAction plugins aren't really designed to be loaded from zip files (this is because they depend on Qt, unlike most other plugin classes) that's why you have to jump through the "actual_plugin" hoops.
I'd suggest running calibre from source and implementing your plugin there. It's fairly trivial to run calibre from source, instructions in the user manual.
Notice to all: I can not
provide assistance with DRM removal, for legal reasons, so please do not contact me about it.