fix: resolve pi binary on Windows (global paths + .cmd/.exe extension handling)

[Varun-Patkar]

Fixes #6

I ran into this on my own system where the extension wouldn't find or launch pi on Windows. I needed it working so I dug in and fixed it. I won't be staying as a maintainer; just contributing this because it was broken for me.

Problem

Two issues on Windows:

1. No Windows global paths checked. The resolver only looked at Unix paths (~/.bun/bin/pi, ~/.local/bin/pi, etc.) and left the Windows global candidates list empty, so pi installed globally via npm/pnpm was never found.

2. Custom path setting hangs the terminal. When setting pi-vscode.path to something like C:\nvm4w\nodejs\pi, the extension tried to spawn that path directly. On Windows, that file is a bash shim (not a Windows executable), so the terminal just hung indefinitely.

Fix

• Added %APPDATA%\npm and %LOCALAPPDATA%\pnpm as Windows global candidate directories, checking for pi.cmd, pi.exe, and pi.ps1.
• When a custom path is provided on Windows without a recognized executable extension, the resolver now probes for .cmd/.exe/.ps1 variants and uses the first one that exists on disk.
• Added 6 new test cases covering both fixes.

[Varun-Patkar]

Hi @pi0 /any other maintainers,
Could this PR be reviewed and merged?

[pi0]

thnx!