Special case reticulate for the old supervisor (#5438)

This special cases reticulate so the Python session is started with the
old jupyter supervisor while we don't implement
#5226

If we don't do this, reticulate will try to use the new supervisor
(because it forwards to `PythonRuntimeSession.start()`)
and users will see a:


![image](https://github.com/user-attachments/assets/8f652b87-9a85-4bc4-952f-f33f0e3309b5)


```
socket hang up
```

### QA Notes

Now reticulate should work even if Positron is configured to use the new
supervisor:


![image](https://github.com/user-attachments/assets/96518697-88ad-4963-a017-7e294660a002)

extensions/positron-python/src/client/positron/session.ts

@@ -437,7 +437,7 @@ export class PythonRuntimeSession implements positron.LanguageRuntimeSession, vs
 
     private async createKernel(): Promise<JupyterLanguageRuntimeSession> {
         const config = vscode.workspace.getConfiguration('positronKernelSupervisor');
-        if (config.get<boolean>('enable', true)) {
+        if (config.get<boolean>('enable', true) && this.runtimeMetadata.runtimeId !== 'reticulate') {
             // Use the Positron kernel supervisor if enabled
             const ext = vscode.extensions.getExtension('vscode.positron-supervisor');
             if (!ext) {