Summary

• Fixes Too narrow type hint for validate() #19112 - Return type annotation for Validator::validate() is too restrictive

The return type array<string, array<string, string>> didn't account for nested validators. When using addNested() or addNestedMany(), the error values can be nested arrays, not just strings.

Example with nested validator:

$validator->addNested('address', $addressValidator);

Error structure when nested validation fails:

[
    'address' => [
        'street' => ['_required' => 'This field is required'],
        'city' => ['_required' => 'This field is required'],
    ]
]

The inner values are array<string, string>, not string.

Fix: Updated return type to array<string, array<string, string|array>> which accurately reflects the actual return structure when nested validators are used.