Updated user agent string formats to match backend parser requirements

[Chriztiaan]

For context, the current user agent strings are not parsed successfully and end up as "unknown" on the current and last 30 days connected device charts in the new dashboard.

Documented examples:

powersync-dart/1.6.4 Dart/3.4.2 linux
powersync-dart/1.6.4 Dart/3.4.2 android/34
powersync-dart/1.6.4 Dart (flutter-web) Chrome/128 android
powersync-js/1.16.2 powersync-react-native/1.11.0 react-native/0.78 android/34
powersync-js/1.16.2 powersync-web/1.6.0 Chrome/128 android

Proof of success:

Screenshots