### What does this PR do?
Previously, 'bun whoami' showed a reservation message indicating it was
reserved for future use. This change updates the command to execute 'bun
pm whoami' directly, making it consistent with npm's behavior.
Fixes#22614
Changes:
- Route 'bun whoami' to PackageManagerCommand instead of ReservedCommand
- Update PackageManagerCommand.exec to handle direct 'whoami' invocation
### How did you verify your code works?
- Add tests to verify both 'bun whoami' and 'bun pm whoami' work
correctly
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Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
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