v0.4.0 of pubup

Automatically update pubspec.yaml dependency constraints to the latest resolvable versions across Dart and Flutter workspace packages. Changelog excerpt: - **Workspace-coordinated updates.**When the root pubspec.yamldeclares a workspace:list, pubup now updates shared dependencies atomically across all members that declare them: constraints are rewritten in every affected pubspec.yaml, then a single root-level pub getvalidates the workspace graph. This fixes the failure mode where per-package pub addcalls left the workspace in a contradictory intermediate state (e.g. root on very_good_analysis ^10while members still pin ^6). - Non-wo[...]