Add function to fetch runnable at cursor position

[ERoydev]

Expose a command in the extension that provides an interface for fetching a specific Runnable from the LSP. This lets the user select a Runnable directly instead of using the debug command, which currently prompts them to choose between multiple runnables. The fetched Runnable can then be used to call the debugSingle command directly.

Open to suggestions if there’s existing functionality that already provides this.

Here’s an example of the behavior I’m trying to address::