feat(LEMS-4171): Update answer area to include calculator variant (#3780)

## Summary
- `packages/perseus-core/src/data-schema.ts` — adds CalculatorVariant type ("scientific" | "graphing" | "four_function") and extends PerseusAnswerArea with calculatorVariant: CalculatorVariant | null
- `packages/perseus-core/src/parse-perseus-json/perseus-parsers/perseus-answer-area.ts` — adds calculatorVariant field to parser using nullable(enumeration(...)) for strict validation; migrates legacy calculator: true content to calculatorVariant: "scientific" on parse
- `packages/perseus-core/src/utils/get-default-answer-area.ts` — includes `calculatorVariant: null` in the default answer area
- `packages/perseus-editor/src/item-extras-editor.tsx` — converts flat "Show calculator" checkbox into an expandable group matching the financial calculator pattern; selecting the parent defaults to scientific; sub-options behave as mutually exclusive radio buttons
- Remaining files add `calculatorVariant:null` to tests

### Notes
- The legacy calculator boolean is preserved and kept in sync for backward compatibility while the frontend migrates
- Existing content without calculatorVariant defaults to null (or "scientific" if calculator: true)

[Associated Webapp Change](Khan/webapp#40228)

Issue: LEMS-4171

## Test plan:
Validated with [ZND](https://prod-znd-260616-12526-c35f366.khanacademy.org/math/ap-statistics/bivariate-data-ap/least-squares-regression/e/calculating-equation-least-squares)
### Scenarios tested

- [x] Unchecked `Show Calculator` doesn't show Calculator button
- [x] Checked defaults to `Scientific`
- [x] Changing from default to Graphing shows graphing
- [x] Changing to four function shows four function

https://github.com/user-attachments/assets/55c08478-508b-4c62-8232-50160b5f821c

Author: anakaren-rojas

Reviewers: jeremywiebe, anakaren-rojas

Required Reviewers:

Approved By: jeremywiebe

Checks: ⏭️  1 check has been skipped, ✅ 11 checks were successful

Pull Request URL: #3780

Author: anakaren-rojas

.changeset/angry-meals-sing.md

@@ -0,0 +1,7 @@
+---
+"@khanacademy/perseus": minor
+"@khanacademy/perseus-core": minor
+"@khanacademy/perseus-editor": minor
+---
+
+Updates answer area to include calculator variant

packages/perseus-core/src/data-schema.ts

@@ -360,7 +360,12 @@ export const ItemExtras = [
      */
     "periodicTableWithKey",
 ] as const;
-export type PerseusAnswerArea = Record<(typeof ItemExtras)[number], boolean>;
+
+export type CalculatorVariant = "scientific" | "graphing" | "four_function";
+
+export type PerseusAnswerArea = Record<(typeof ItemExtras)[number], boolean> & {
+    calculatorVariant: CalculatorVariant | null;
+};
 
 /**
  * The type representing the common structure of all widget's options. The

packages/perseus-core/src/feature-flags.ts

@@ -12,6 +12,7 @@
 const PerseusFeatureFlags = [
     "input-number-to-numeric-input", // TODO(LEMS-4085): clean up feature flag
     "grapher-to-interactive-graph", // TODO(LEMS-4259): clean up feature flag
+    "desmos-calculator", // TODO(LEMS-4180): clean up feature flag
 ] as const;
 
 export default PerseusFeatureFlags;

packages/perseus-core/src/parse-perseus-json/perseus-parsers/perseus-answer-area.test.ts

@@ -10,6 +10,7 @@ import type {PerseusAnswerArea} from "../../data-schema";
 describe("parsePerseusAnswerArea", () => {
     const allFalse: PerseusAnswerArea = {
         calculator: false,
+        calculatorVariant: null,
         financialCalculatorMonthlyPayment: false,
         financialCalculatorTotalAmount: false,
         financialCalculatorTimeToPayOff: false,
@@ -25,6 +26,7 @@ describe("parsePerseusAnswerArea", () => {
     it("keeps `true` values", () => {
         const allTrue: PerseusAnswerArea = {
             calculator: true,
+            calculatorVariant: "scientific",
             financialCalculatorMonthlyPayment: true,
             financialCalculatorTotalAmount: true,
             financialCalculatorTimeToPayOff: true,

packages/perseus-core/src/parse-perseus-json/perseus-parsers/perseus-answer-area.ts

@@ -1,10 +1,25 @@
-import {boolean, defaulted, object} from "../general-purpose-parsers";
+import {
+    boolean,
+    defaulted,
+    enumeration,
+    nullable,
+    object,
+    pipeParsers,
+} from "../general-purpose-parsers";
+import {convert} from "../general-purpose-parsers/convert";
+
+type CalculatorVariant = "scientific" | "graphing" | "four_function";
 
 const booleanOrFalse = defaulted(boolean, () => false);
+const nullableCalculatorVariant = defaulted(
+    nullable(enumeration("scientific", "graphing", "four_function")),
+    () => null,
+);
 
-export const parsePerseusAnswerArea = defaulted(
+const baseParser = defaulted(
     object({
         calculator: booleanOrFalse,
+        calculatorVariant: nullableCalculatorVariant,
         financialCalculatorMonthlyPayment: booleanOrFalse,
         financialCalculatorTotalAmount: booleanOrFalse,
         financialCalculatorTimeToPayOff: booleanOrFalse,
@@ -13,10 +28,22 @@ export const parsePerseusAnswerArea = defaulted(
     }),
     () => ({
         calculator: false,
+        calculatorVariant: null,
         financialCalculatorMonthlyPayment: false,
         financialCalculatorTotalAmount: false,
         financialCalculatorTimeToPayOff: false,
         periodicTable: false,
         periodicTableWithKey: false,
     }),
 );
+
+export const parsePerseusAnswerArea = pipeParsers(baseParser).then(
+    convert((parsed) => {
+        const calculatorVariant: CalculatorVariant | null =
+            parsed.calculator && parsed.calculatorVariant === null
+                ? "scientific"
+                : parsed.calculatorVariant;
+
+        return {...parsed, calculatorVariant};
+    }),
+).parser;