fix(powershell): display search stderr (#3146)

This shows stderr output from `atuin search -i` in PowerShell:

The output looks like this:
<img width="628" height="149" alt="image"
src="https://github.com/user-attachments/assets/c0a4bc9a-5d57-415f-a5b4-9c497744c6e0"
/>


Currently reproducible with the following config:
```toml
[keymap.emacs]
"foo" = "bar"
"=" = "bar"
```

I started by using `Start-Process` in the first commit, but then rewrote
it entirely as using a `Process` object directly should be more stable
(`Start-Process` already [caused
issues](https://github.com/atuinsh/atuin/pull/2543#issuecomment-2647555114)
in the past).

This fixes the PowerShell part of #3134

## Checks
- [x] I am happy for maintainers to push small adjustments to this PR,
to speed up the review cycle
- [x] I have checked that there are no existing pull requests for the
same thing

0 files changed, 0 insertions, 0 deletions