Unwrap scalars in shell output mode. (#2548)

* 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

pkg/yqlib/encoder_shellvariables.go

@@ -57,7 +57,13 @@ func (pe *shellVariablesEncoder) doEncode(w *io.Writer, node *CandidateNode, pat
 			// let's just pick a fallback key to use if we are encoding a single scalar
 			nonemptyPath = "value"
 		}
-		_, err := io.WriteString(*w, nonemptyPath+"="+quoteValue(node.Value)+"\n")
+		var valueString string
+		if pe.prefs.UnwrapScalar {
+			valueString = node.Value
+		} else {
+			valueString = quoteValue(node.Value)
+		}
+		_, err := io.WriteString(*w, nonemptyPath+"="+valueString+"\n")
 		return err
 	case SequenceNode:
 		for index, child := range node.Content {