* feat: Add UnwrapScalar to ShellVariablesPreferences
- Add UnwrapScalar boolean field to ShellVariablesPreferences struct.
- Initialize UnwrapScalar to false in NewDefaultShellVariablesPreferences.
- This preference will control whether shell output should be quoted or raw.
* feat: Propagate unwrapScalar to ShellVariablesPreferences
- In configureEncoder function, set UnwrapScalar in ConfiguredShellVariablesPreferences.
- This ensures the -r flag's state is passed to the shell encoder for raw output control.
* feat: Implement conditional quoting in shellVariablesEncoder
- Modify doEncode method to check pe.prefs.UnwrapScalar.
- If UnwrapScalar is true, output raw node.Value.
- Otherwise, use quoteValue for shell-safe quoting.
- This enables quote-free output for Kubernetes workflows when -r is used.
* test: Add tests for UnwrapScalar in shell encoder
- Introduce assertEncodesToUnwrapped helper function.
- Add TestShellVariablesEncoderUnwrapScalar to verify quote-free output with -r.
- Add TestShellVariablesEncoderDefaultQuoting to confirm default quoting behavior without -r.
- Ensure comprehensive testing of conditional quoting logic for shell output.
* remove redundant test
