Add `--dry-run` flag to `uv pip install` (#1436)
## What
Adds a `--dry-run` flag that ejects out of the installation process
early (but after resolution) and displays only what *would have*
installed
## Closes
Closes #1244
## Out of Scope
I think it may be nice to include a `dry-run` flag for `uninstall` even
though `pip` doesn't implement this... thinking `Would uninstall X
packages: ...`
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Co-authored-by: Zanie Blue <contact@zanie.dev>
