fix: Prevent a deadlock waiting for browser debugger to attach

[Alanoll]

#702 fixed the fact that the debugger never attached to projects using the project style configuration, but I found in my larger repo's that a potential deadlock could occur waiting for the debugger to attach.

Scenario:
The RPC event onBrowserDebug is sent as soon as VSCode completes it's promise to attach to the browser in the then. There's a timing issue if the browser hasn't yet executed the setupFile from the extension that triggers the await for the event.

So:

1. Start Debug
2. Extension launches debug session for VSCode to attach to the browser
3. Vitest spins up the test project and initializes
4. VSCode completes attaching and triggers onBrowserDebug event
5. Browser loads the setupFile browserSetupFile.ts that await for the onBrowserEvent via the __vscode_waitForDebugger command created here

Because the event fired before the setupfile started to listen, the debug session deadlocks here waiting for the signal.

This PR starts listening to the event before adding the setupFile to the project collection, and stores the state in a private variable. The Command now checks this variable first to see if it's already attached (and immediately returns) or subscribes to the event again like it was doing before to resolve the promise.

[Alanoll]

@sheremet-va This (if approved) I think might need to be in the same release as #702

[sheremet-va]

I would expect __vscode_waitForDebugger to throw an error if fullfilled is false. This PR will still wait indefinitely. Maybe have debuggerAttached as undefined by default

[Alanoll]

Give it a look now. I've added the undefined to checks so it'll treat a false value as "VSCode has already failed to attach"

I followed the already existing pattern to reject the promise with an error.