fix: isObject should return false for functions

[chatman-media]

Bug

The isObject / @IsObject() validator incorrectly accepts function values as valid objects.

The README documentation is explicit (emphasis mine):

@IsObject() — Checks if the object is valid Object (null, functions, arrays will return false).

However, the implementation in src/decorator/typechecker/IsObject.ts includes typeof value === 'function' in the condition:

// before
return value != null && (typeof value === 'object' || typeof value === 'function') && !Array.isArray(value);

This causes isObject(() => 'x') to return true, which contradicts the documented behavior.

Closes #2515

Root cause

The || typeof value === 'function' branch was included in the check, presumably to mirror a generic "non-primitive" guard. Since functions are not plain data objects, the docs correctly exclude them — the implementation just didn't follow through.

Fix

Remove the typeof value === 'function' branch:

// after
return value != null && typeof value === 'object' && !Array.isArray(value);

Test evidence

Two function values (() => 'function' and a named function expression) were added to the invalidValues array in the IsObject test suite. Before the fix, 2 tests failed; after the fix, all 5 IsObject tests pass and the full suite (806 tests) continues to pass.

PASS test/functional/validation-functions-and-decorators.spec.ts
  IsObject
    ✓ should not fail if validator.validate said that its valid
    ✓ should fail if validator.validate said that its invalid
    ✓ should not fail if method in validator said that its valid
    ✓ should fail if method in validator said that its invalid
    ✓ should return error object with proper data

Tests: 806 passed, 806 total