Improve connection status

[rkistner]

Changes to SyncStatus:

• Fix connected not updating when calling powersync.disconnect().
• Add connecting, downloading and uploading flags.
• Add downloadError, uploadError and a combined anyError field.

The demo now uses these to provide more fine-grained connectivity status.

Also includes a minor fix for error parsing that would only return the first character of the error message in some cases.

[DominicGBauer]

Based on all the repeated changes should we not just create a common component for that status bar and then have all the demos use it?

[rkistner]

Technically the status bar is slightly different between demos (one contains search), but the status icon is the same and could be re-used.

I'm a little conflicted on this one: One the one side a common package would allow us to re-use code between the demos, but on the other side it makes it more difficult for others to copy and modify a demo.

What I think would actually be best is to reduce the scope of some of the demos (specifically supabase-anonymous-auth and supabase-edge-auth) to not contain the entire todolist app, but rather just a minimal amount of code to show how to use custom auth functions.

[DominicGBauer]

Yeah that makes sense. I left the status bar in the auth demos because of the status icon mainly but don't think it's really necessary