Don't require priority on checksum

Author: simolus3

packages/powersync_core/lib/src/sync_types.dart

@@ -166,7 +166,10 @@ class BucketChecksum {
 
   BucketChecksum.fromJson(Map<String, dynamic> json)
       : bucket = json['bucket'] as String,
-        priority = json['priority'] as int,
+        // Use the default priority (3) as a fallback if the server doesn't send
+        // priorities. This value is arbitrary though, it won't get used since
+        // servers not sending priorities also won't send partial checkpoints.
+        priority = json['priority'] as int? ?? 3,
         checksum = json['checksum'] as int,
         count = json['count'] as int?,
         lastOpId = json['last_op_id'] as String?;

packages/powersync_core/test/in_memory_sync_test.dart

@@ -75,11 +75,15 @@ void main() {
       final status = await waitForConnection();
 
       syncService.addLine({
-        'checkpoint': Checkpoint(
-          lastOpId: '0',
-          writeCheckpoint: null,
-          checksums: [BucketChecksum(bucket: 'bkt', priority: 1, checksum: 0)],
-        )
+        'checkpoint': {
+          'last_op_id': '0',
+          'buckets': [
+            {
+              'bucket': 'bkt',
+              'checksum': 0,
+            }
+          ],
+        },
       });
       await expectLater(status, emits(isSyncStatus(downloading: true)));