Setup run through bunx or bun x registered the bin inside bun's temporary
package cache. Detect bun's package-runner launch from npm_command=exec
with a bun user agent and register the pinned bunx launcher, wrapped in
cmd.exe on Windows like the npx launcher. Doctor, update maintenance and
uninstall recognize it as REA-owned, and setup's printed commands name
the runner that launched it.
Read the runner variables case-insensitively on Windows, where the CLI
environment snapshot upper-cases variable names and setup run through
npx also fell back to the cache path.
Co-authored-by: morluto <76467478+morluto@users.noreply.github.com>
