Add proposal-decimal dependency and fix method calls

- Add proposal-decimal to devDependencies
- Fix isNaN and isFinite method calls

Author: jessealama

docs/data-model.md

@@ -25,7 +25,7 @@ Decimal has a single, quiet NaN value, similar to JS's Number:
 
 ```javascript
 const nan = new Decimal("NaN");
-nan.isNaN; // => true
+nan.isNaN(); // => true
 
 // NaN propagates through operations
 nan.add(new Decimal("5")); // => NaN
@@ -40,7 +40,7 @@ Positive and negative infinity are supported:
 const posInf = new Decimal("Infinity");
 const negInf = new Decimal("-Infinity");
 
-posInf.isFinite; // => false
+posInf.isFinite(); // => false
 posInf.add(new Decimal("1")); // => Infinity
 posInf.negate(); // => -Infinity
 ```

package-lock.json

@@ -28,15 +28,14 @@
     "url": "https://github.com/tc39/proposal-decimal/issues"
   },
   "homepage": "https://tc39.es/proposal-decimal/",
-  "dependencies": {
-  },
   "devDependencies": {
     "@tc39/ecma262-biblio": "2.1",
     "@tc39/ecma402-biblio": "^2.1.1050",
     "ecmarkup": "github:jessealama/ecmarkup#permit-decimal-subscript-D",
     "marked": "^15.0.12",
     "mkdirp": "^3.0.1",
     "prettier": "^3.6.2",
-    "prismjs": "^1.30.0"
+    "prismjs": "^1.30.0",
+    "proposal-decimal": "^20250613.0.0"
   }
 }