Draft: Add PEP-484 type annotations to generator and code

As I had to touch almost every line I took the opportunity to also cleanup the code, as this simplified the task: I used mypy and flake8 a lot during development and every warning was distracting me from getting the thing done.

While doing that I also stumbled over lots of smaller problems and even bugs; they are at the start of the queue so feel free to fast-track them by only merging them or cherry-picking them.

This addresses python/typeshed#4310 by adding the type information into the library instead of carrying them as as separate files in a separate project. If you want to use the for previous information, look at my typeshed for libvirt.

This task was already announced once at https://patchew.org/Libvirt/cover.1587993402.git.hahn@univention.de/, which becomes obsolete with the pull-request.

• there are some TODOs in c3b26fcc
• maybe also create *.pyi stubs for libvirtmod*.so
• extend libvirt-api.xml to return more specific Python types like List[int] - see comments
• verify that my type annotations matches the actual returned data by calling each function from some (manually generated?) unit test file

examples/consolecallback.py

@@ -41,7 +41,7 @@ def check_console(console: Console) -> bool:
     if (console.state[0] == libvirt.VIR_DOMAIN_RUNNING or console.state[0] == libvirt.VIR_DOMAIN_PAUSED):
         if console.stream is None:
             console.stream = console.connection.newStream(libvirt.VIR_STREAM_NONBLOCK)
-            console.domain.openConsole(None, console.stream, 0)
+            console.domain.openConsole(None, console.stream, 0)  # type: ignore  # FIXME
             console.stream.eventAddCallback(libvirt.VIR_STREAM_EVENT_READABLE, stream_callback, console)
     else:
         if console.stream: