refactor: Replace drift by serverpod as core engine (#33)

packages/serverpod_offline_sync_server/lib/serverpod_offline_sync_server.dart

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+export 'package:serverpod_offline_sync_client/serverpod_offline_sync_client.dart';
+
+export 'src/generated/endpoints.dart';
+
+// The models are exported by the client package to ensure the same class as the
+// one expected by the functions.
+// export 'src/generated/protocol.dart';

packages/serverpod_offline_sync_server/lib/src/endpoints/module_endpoint.dart

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+// import 'package:serverpod/serverpod.dart';
+// import 'package:serverpod_offline_sync_shared/serverpod_offline_sync_shared.dart';
+
+// // import '../generated/protocol.dart';
+
+// /// TODO: Create the classes.
+// abstract class CrdtDataEntry {}
+
+// /// Endpoint for the CRDT sync.
+// class SyncOfflineChangesEndpoint extends Endpoint {
+//   @override
+//   bool get requireLogin => true;
+
+//   /// Syncs the offline changes between server and client.
+//   ///
+//   /// This endpoint is used to sync the offline changes between server and
+//   /// client. After a handshake on the [migrationVersion] to ensure that the
+//   /// merge can happen, the client will send all [offlineChanges] since the
+//   /// [lastSyncHlc] HLC and the server will send all online changes through
+//   /// the returning stream.
+//   ///
+//   /// The connection will be kept open until one end disconnects, forwarding
+//   /// the changes to the other end.
+//   Stream<CrdtDataEntry> syncOfflineChanges(
+//     Session session, {
+//     required String migrationVersion,
+//     required Hlc lastSyncHlc,
+
+//     /// TODO: Create the classes.
+//     /// CrdtDataEntry will be a sealed class with the changes.
+//     ///
+//     /// - CrdtDataRow: New rows inserted.
+//     /// - CrdtDataField: Fields updated.
+//     /// - CrdtDataDeleted: Rows deleted.
+//     required Stream<CrdtDataEntry> offlineChanges,
+//   }) async* {
+//     // TODO: Implement the business layer for the CRDT sync.
+//     // yield* CrdtSync.syncOfflineChanges(session);
+//   }
+// }

packages/serverpod_offline_sync_server/lib/src/models/data/deleted.spy.yaml

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+### CRDT tombstone table.
+###
+### This table stores all tombstones for deleted data.
+class: CrdtDataDeleted
+extends: BaseHlc
+table: crdt_data_tombstone
+database: all
+fields:
+  ### Row that was deleted.
+  row: CrdtDataRow?, relation(name=row_deleted, field=rowId, onDelete=Cascade)
+  rowId: int
+
+  ### The node that updated the field.
+  node: CrdtNode?, relation
+
+  ### When the row was deleted.
+  isDeleted: bool
+
+indexes:
+  crdt_data_tombstone_row_idx:
+    fields: rowId
+    unique: true

packages/serverpod_offline_sync_server/lib/src/models/data/field.spy.yaml

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+### CRDT data table.
+###
+### This table stores only the HLC timestamp for a field. During merge, if the
+### other HLC is greater, the actual data must be fetched from the table itself.
+class: CrdtDataField
+extends: BaseHlc
+table: crdt_data_fields
+database: all
+fields:
+  ### Row that the field belongs to.
+  row: CrdtDataRow?, relation(name=row_fields, onDelete=Cascade)
+
+  ### Column that the field belongs to.
+  column: CrdtSchemaColumn?, relation(onDelete=Cascade)
+
+  ### The node that updated the field.
+  node: CrdtNode?, relation
+
+indexes:
+  crdt_data_fields_row_column_idx:
+    fields: rowId, columnId
+    unique: true

packages/serverpod_offline_sync_server/lib/src/models/data/row.spy.yaml

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+### CRDT data rows table.
+###
+### This table stores the data for all tables that are registered for CRDT
+### synchronization. It is used to interact with the CRDT data.
+###
+### The row is also the HLC timestamp for when it was inserted. This is used to
+### avoid creating one entry per field until a field is updated.
+class: CrdtDataRow
+extends: BaseHlc
+table: crdt_data_rows
+database: all
+fields:
+  ### Identifier for the user or client that owns the data.
+  user: CrdtUser?, relation(onDelete=Cascade)
+
+  ### Reference to the table this row belongs to.
+  tbl: CrdtSchemaTable?, relation(onDelete=Cascade)
+
+  ### Row identifier.
+  uuidRowId: UuidValue
+
+  ### The node that inserted the row with the HLC timestamp.
+  node: CrdtNode?, relation
+
+  ### The tombstone for this row.
+  deleted: CrdtDataDeleted?, relation(name=row_deleted, optional)
+
+  ### The fields for this row.
+  fields: List<CrdtDataField>?, relation(name=row_fields)
+
+indexes:
+  crdt_data_rows_user_tbl_row_idx:
+    fields: userId, tblId, uuidRowId
+    unique: true

packages/serverpod_offline_sync_server/lib/src/models/node/node.spy.yaml

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+### CRDT nodes table.
+###
+### This table stores all nodes that have been seen.
+class: CrdtNode
+table: crdt_nodes
+database: all
+fields:
+  ### The user that owns the node.
+  user: CrdtUser?, relation(name=user_nodes, onDelete=Cascade)
+
+  ### Unique identifier for the node.
+  uuidNodeId: UuidValue, default=random_v7, unique
+
+  # TODO: Make this non-nullable once the migration version is implemented.
+  ### The migration version of the CRDT data that the node has seen.
+  lastSeenMigrationVersion: String?
+
+  ### The last HLC timestamp when the node has synchronized.
+  lastReceivedHlc: Hlc?

packages/serverpod_offline_sync_server/lib/src/models/node/user.spy.yaml

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+### CRDT users table.
+###
+### Normalized storage for user IDs. The normalized data table references this
+### by integer id instead of storing the user id string.
+class: CrdtUser
+table: crdt_users
+database: all
+fields:
+  ### User identifier string.
+  uuidUserId: UuidValue, default=random_v7, unique
+
+  ### The current node id of the user.
+  currentNode: CrdtNode?, relation(optional)
+
+  ### The nodes associated with the user.
+  nodes: List<CrdtNode>?, relation(name=user_nodes)

packages/serverpod_offline_sync_server/lib/src/models/schema/column.spy.yaml

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+### CRDT schema columns table.
+class: CrdtSchemaColumn
+table: crdt_schema_columns
+database: all
+fields:
+  ### Reference to the table this column belongs to.
+  tbl: CrdtSchemaTable?, relation(onDelete=Cascade)
+
+  ### Name of the column.
+  name: String
+
+indexes:
+  crdt_schema_columns_table_column_idx:
+    fields: tblId, name
+    unique: true

packages/serverpod_offline_sync_server/lib/src/models/schema/table.spy.yaml

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+### CRDT schema tables table.
+class: CrdtSchemaTable
+table: crdt_schema_tables
+database: all
+fields:
+  ### Name of the synchronized table.
+  name: String, unique