feat(remote): add ability to pass callbacks as arguments

lib/src/callbacks.dart

@@ -0,0 +1,25 @@
+import 'oid.dart';
+import 'remote.dart';
+
+class Callbacks {
+  const Callbacks({
+    this.transferProgress,
+    this.sidebandProgress,
+    this.updateTips,
+    this.pushUpdateReference,
+  });
+
+  /// Callback function that reports transfer progress.
+  final void Function(TransferProgress)? transferProgress;
+
+  /// Callback function that reports textual progress from the remote.
+  final void Function(String)? sidebandProgress;
+
+  /// Callback function matching the `void Function(String refname, Oid old, Oid new)`
+  /// that report reference updates.
+  final void Function(String, Oid, Oid)? updateTips;
+
+  /// Callback function matching the `void Function(String refname, String message)`
+  /// used to inform of the update status from the remote.
+  final void Function(String, String)? pushUpdateReference;
+}