The VSCode extension can now send `ScopesRequest`s and `VariablesRequest`s, and the shell parses and handles them currently with a stubbed response from the server debugger. This demonstrates the roundtrip mechanics and infrastructure, but leaves the implementation of getting actual variables for a separate PR (this one added enough on its own).

<img width="925" height="267" alt="image" src="https://github.com/user-attachments/assets/095a8e0e-6128-468d-976d-c1ff6326dda0" />