Move off simpleplugin

[stuaxo]

Hi,
I got claude to start a branch to move off simpleplugin.

stuaxo#5

Simpleplugin development stopped years ago, removing it is one step towards modernisation.
It would be good if you could sanity check it.
It looks like this basically moves all the big code out of main.py and service.py and uses the native APIs not the ones simpleplugin provided.

I still need to make some time to test this myself, so am not suggesting merging right now, but eyeballs would be good.

Once this is good then the next thing would probably be to move to py-opensonic as those bindings are up to date.

With those two it should be a a good place to add missing features.

One thing about all this is that it will change APIs and move code around, so any outstanding PRs would need bigger changes to merge - so it might make sense to merge any of those before.

Cheers
S