process settings tab messages in a separate thread [CPP-405]

[notoriaga]

As the title suggests this makes the settings client run in a different thread than the main process_messages loop. This should fix the issue of the whole app freezing if the settings request bugs out. Obviously this doesn't fix whatever the underlying issue we are running into is, but this might be a good idea just in case.

Also switches to the native rust settings library here - swift-nav/libsettings-rs#15

[notoriaga]

Have not seen it hang for a while using this - swift-nav/libsettings-rs#15

[john-michaelburke]

[silverjam]

@notoriaga @john-michaelburke Assuming we need to, can we update the threading diagram here: https://github.com/swift-nav/swift-toolbox/blob/main/docs/DESIGN.md#backend-threads-diagram? Also noticed that we don't have the source for that diagram in GitHub, draw.io supports storing/pulling files from GitHub, so we should give that a try.

[notoriaga]

@notoriaga @john-michaelburke Assuming we need to, can we update the threading diagram here: https://github.com/swift-nav/swift-toolbox/blob/main/docs/DESIGN.md#backend-threads-diagram? Also noticed that we don't have the source for that diagram in GitHub, draw.io supports storing/pulling files from GitHub, so we should give that a try.

Nice I'll check it out/update it