feat(vscode): ability to stop server

[benfdking]

No description provided.

[Copilot]

Pull Request Overview

This PR implements a new feature to stop the LSP server within the VSCode extension.

• Adds a new test to verify the stop server functionality.
• Introduces a new command and its implementation to stop the LSP server.
• Updates the package.json to register the new "SQLMesh: Stop Server" command.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
vscode/extension/tests/stop.spec.ts	New test verifying the stop server functionality.
vscode/extension/src/extension.ts	Imports and registers the new stop command.
vscode/extension/src/commands/stop.ts	Implements stop command to stop the LSP server.
vscode/extension/package.json	Registers the stop command in the extension menu.