fix: isObject should return false for functions

The `isObject` function incorrectly returned `true` for function values
because it checked `typeof value === 'function'` in addition to
`typeof value === 'object'`. The README documentation explicitly states
that functions should return false, but the implementation contradicted
this.

Fixes #2515

Author: chatman-media

src/decorator/typechecker/IsObject.ts

@@ -8,7 +8,7 @@ export const IS_OBJECT = 'isObject';
  * Returns false if the value is not an object.
  */
 export function isObject<T = object>(value: unknown): value is T {
-  return value != null && (typeof value === 'object' || typeof value === 'function') && !Array.isArray(value);
+  return value != null && typeof value === 'object' && !Array.isArray(value);
 }
 
 /**

test/functional/validation-functions-and-decorators.spec.ts

@@ -3166,6 +3166,10 @@ describe('IsObject', () => {
     '[]',
     [],
     [{ key: 'value' }],
+    () => 'function',
+    function namedFn() {
+      return 'named function';
+    },
   ];
 
   class MyClass {