Sync progress status

[simolus3]

This extends SyncStatus to report download progress as it happens. Progress is reported as a (completed, total, fraction) triple (where fraction = completed / total) and available:

1. For entire sync operations: db.currentStatus.downloadProgress.untilCompletion.
2. For the progress until a specific priority: db.currentStatus.downloadProgress.untilPriority(myPrio).

The best way to get a look and feel for the API may be to look at this example usage:

powersync.dart/demos/supabase-todolist/lib/widgets/guard_by_sync.dart

Lines 26 to 53 in 9d45ba3

	final status = snapshot.requireData;
	final (didSync, progress) = switch (priority) {
	null => (
	status.hasSynced ?? false,
	status.downloadProgress?.untilCompletion
	),
	var priority? => (
	status.statusForPriority(priority).hasSynced ?? false,
	status.downloadProgress?.untilPriority(priority)
	),
	};
	if (didSync) {
	return child;
	} else {
	return Center(
	child: Column(
	children: [
	const Text('Busy with sync...'),
	LinearProgressIndicator(value: progress?.fraction),
	if (progress case final progress?)
	Text('${progress.completed} out of ${progress.total}')
	],
	),
	);
	}
	},
	);

In an actual app, it looks like this:

Bildschirmaufnahme.2025-03-31.um.13.27.20.mov

There is some delay in the sync_local commit not included in the progress bar now, but the amount of operations is updated as it should be.

[rkistner]

I'm happy with the overall structure & apis - just added some implementation comments.

[rkistner]

I didn't check the details of the sync status refactoring, but I'm happy with the overall approach.