Reloading or restarting VS Code should restart the MCP servers

[karthiknadig]

Testing: #244526

Reloading the project does not automatically restart the server. The tools seems to be cached, but the server handling the tools is not started or restarted.

[connor4312]

This is intentional. We don't want to eagerly start every MCP server to avoid unnecessary resource consumption, and so we cache the last-seen tools and only start the server on-demand if the model asks to use one of the tools (or if the user manually starts it)