Don't clean up extension if extension isntall fails

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Is your feature request related to a problem? Please describe the problem.

When running `iex "& { $(irm https://aspire.dev/install.ps1) } -InstallExtension -Quality dev"` I hit a problem with my corporate policy blocking the extension.

I wanted to do some further inspection on the extension to see waht values I need to allow list, but the script deleted the extension from the temporary directory before I could do so.

```
WARNING: Failed to install VS Code extension: Extension installation failed with exit code 1: Installing extensions... Error: This extension cannot be installed because it is not in the [allowed list](command:workbench.action.openSettings?%255B%257B%2522query%2522%253A%2522%2540id%253Aextensions.allowed%2522%257D%255D) at ro.install (file:///C:/Users/alexanderc/AppData/Local/Programs/Microsoft%20VS%20Code/df53daabb1/resources/app/out/vs/code/node/cliProcessMain.js:464:39767) at process.processTicksAndRejections (node:internal/process/task_queues:104:5) at async Wn.installVSIX (file:///C:/Users/alexanderc/AppData/Local/Programs/Microsoft%20VS%20Code/df53daabb1/resources/app/out/vs/code/node/cliProcessMain.js:457:1087) at async file:///C:/Users/alexanderc/AppData/Local/Programs/Microsoft%20VS%20Code/df53daabb1/resources/app/out/vs/code/node/cliProcessMain.js:456:2216 at async Promise.all (index 0) at async Wn.installExtensions (file:///C:/Users/alexanderc/AppData/Local/Programs/Microsoft%20VS%20Code/df53daabb1/resources/app/out/vs/code/node/cliProcessMain.js:456:2153) at async file:///C:/Users/alexanderc/AppData/Local/Programs/Microsoft%20VS%20Code/df53daabb1/resources/app/out/vs/code/node/cliProcessMain.js:493:59119 at async Module.PK (file:///C:/Users/alexanderc/AppData/Local/Programs/Microsoft%20VS%20Code/df53daabb1/resources/app/out/vs/code/node/cliProcessMain.js:493:63094) at async As (file:///C:/Users/alexanderc/AppData/Local/Programs/Microsoft%20VS%20Code/df53daabb1/resources/app/out/cli.js:433:70559) Failed Installing Extensions: file:///c%3A/Users/alexanderc/AppData/Local/Temp/aspire-extension-fbb42f17/aspire-vscode-1.17.0.vsix
WARNING: The CLI was installed successfully, but the extension installation failed
```

### Describe the solution you'd like

If extension install fails, don't auto remove the extension to allow further investigation.

### Additional context

_No response_

Start with install.ps1 and trace the -InstallExtension path invoked by the reported PowerShell command, focusing on cleanup after the VS Code extension installation fails. Reproduce the blocked-install case and verify that the .vsix remains in the temporary directory while the CLI still reports the installation failure.

Written by the indexing model from the issue text.