- Added `args` field to ShellResult to capture the executed command.
- Added `exit_code` property to ShellResult as an alias for `returncode`.
- Added `check_returncode()` method to ShellResult to raise CalledProcessError on non-zero exit codes.
- Renamed `code` field to `returncode` in ShellResult with backward-compatible `code` property.
- Updated `run()` command documentation to clarify available ShellResult fields.