Replace GBulb with PyGObject's native asyncio handling

[freakboy3742]

PyGObject has an in-development branch adding native asyncio integration. This PR replaces GBulb with that branch.

At this point, this is an experiment to provide testing feedback upstream; it is unlikely we'll adopt this before PyGObject merges the branch.

Refs #2548 (an alternate PR removing gbulb)

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[rmartin16]

PyGObject==3.50.0 released today. Unfortunately, gbulb is not compatible with it and Gtk apps crash at launch; PyGObject is now expecting the event loop installed by gbulb to provide a running() method that implements a context manager.

I mention it here because PyGObject merged their native async support which included the change that breaks gbulb. Given this PR is intended to use that new functionality, merging this would remove gbulb and this issue with PyGObject==3.50.0.

[freakboy3742]

Let's do it. I've got no love for maintaining GBulb; the fact that 3.50.0 is backwards incompatible with means there's a good reason to adopt the new API.

It's also promising that the final form of this patch needed a tweak to slow down GTK operation so that the probe can observe changes :-)

[rmartin16]

few questions. i'll test on fedora and arch as well to make sure nothing weird happens.

[rmartin16]

Looks good. Let's send it.