[powershell] investigate ancient chocolatey wizard magic to impl "source HKCU"

Windows has a Better and Worse story for updating PATH:

* Better: you can just modify `HKCU:\Environment\Path` and every windows shell should respect that
* Worse: there is no equivalent to `source ~/.profile` to refresh the current shell (and even opening a new tab in Windows Terminal is insufficient, only opening a new Window will force a reread of HKCU.

Someone told me that chocolatey (at least at some point?) had some dark wizard magic to potentially refresh the local shell's env:

https://github.com/chocolatey-archive/chocolatey/blob/master/src/redirects/RefreshEnv.cmd

If this worked, and especially if it could be done automatically by the powershell installer, this would make windows basically a perfect UX.

I'm suspicious of it but it's worth investigating more deeply.

Start by reviewing Chocolatey's linked RefreshEnv.cmd and the PowerShell installer behavior in cargo-dist. Determine whether the environment can be refreshed in the current shell, whether the approach works reliably, and whether automatic use by the installer is feasible; document the result and any constraints.

Written by the indexing model from the issue text.