update to newer async/await coroutine syntax and minor fixes

[sillygoose]

Here is an update to the more modern async/await syntax you inquired about, plus some other minor fixes suggested by pylint.

Not sure how to test the coroutine changes other than running these changes with my multi-inverter application. I see you have some test code using pytest, I'll have to look into pytest to see what it offers but in the meantime you can consider these changes.

[sillygoose]

This implements the suggested reversion, hope it takes care of the updates.

[kellerza]

Thanks @sillygoose ! 🎉