Update testing.d.ts

Add `Stubscape` export to testing.d.ts and align documentation with
corresponding testing.js code.

testing.d.ts

@@ -18,13 +18,30 @@ import type { Shescape as ShescapeType } from "shescape";
 export const injectionStrings: string[];
 
 /**
- * A test stub of shescape that has the same input-output profile as the real
- * shescape implementation.
+ * An optimistic test stub of Shescape that has the same input-output profile as
+ * the real Shescape implementation.
  *
  * In particular:
+ * - The constructor never fails.
  * - Returns a string for all stringable inputs.
  * - Errors on non-stringable inputs.
- * - Converts non-array inputs to single-item arrays where necessary.
+ * - Errors on non-array inputs where arrays are expected.
+ * - Errors when trying to quote when `shell: false`.
+ */
+export const Stubscape: ShescapeType;
+
+/**
+ * An optimistic test stub of Shescape that has the same input-output profile as
+ * the real Shescape implementation.
+ *
+ * In particular:
+ * - The constructor never fails.
+ * - Returns a string for all stringable inputs.
+ * - Errors on non-stringable inputs.
+ * - Errors on non-array inputs where arrays are expected.
+ * - Errors when trying to quote when `shell: false`.
+ *
+ * @alias Stubscape
  */
 export const Shescape: ShescapeType;