Use Pub Workspaces

[Levi-Lesches]

When the plugin is ready to switch to Dart 3.6.0, we should use a Pub Workspace so dart pub get can be run once for all the packages in the entire repository. It also makes sure that all inter-dependencies are overridden with path dependencies, while the pubspecs are checked to make sure they all point to the right versions. The whole thing can still be compatible with melos.

Mainly, this leads to some pretty big performance improvements with dart pub get and dart analyze as the tooling can have one shared "context" for everything, instead of spinning up new contexts for all the packages and examples.