chore: add development environment setup script and move dependency overrides

Author: mcquenji

pubspec_overrides.dev.yaml

@@ -0,0 +1,5 @@
+# This file is used for development overrides. Run `dart tool/dev.dart` to apply these overrides.
+# `pubspec_overrides.yaml` is ignored by git, so it won't affect CI or other developers.
+dependency_overrides:
+  grumpy_annotations:
+    path: ../grumpy_annotations

tool/dev.dart

@@ -0,0 +1,21 @@
+// this is a tool script so a logging framework is lowkey overkill.
+// ignore_for_file: avoid_print
+
+import 'dart:io';
+
+/// Sets up the development environment by copying `pubspec_overrides.dev.yaml` to `pubspec_overrides.yaml`.
+/// This expects all other packages to be checked out in a sibling directory to the main `grumpy` package.
+void main() async {
+  final src = File('pubspec_overrides.dev.yaml');
+
+  if (!await src.exists()) {
+    print('No pubspec_overrides.dev.yaml found. Skipping.');
+    return;
+  }
+
+  final dst = File('pubspec_overrides.yaml');
+
+  await src.copy(dst.path);
+
+  print('Copied pubspec_overrides.dev.yaml to pubspec_overrides.yaml');
+}