Add validationRules() method to base Dto class

[dereuromark]

Adds a validationRules() method that returns framework-agnostic validation rules extracted from field metadata. This enables framework plugins (CakePHP, Laravel, Symfony) to bridge DTO validation rules to their native validator systems.

Usage

$dto = new UserDto(['name' => 'Test']);
$rules = $dto->validationRules();
// Returns:
// [
//     'name' => ['required' => true, 'minLength' => 2, 'maxLength' => 50],
//     'email' => ['required' => true, 'pattern' => '/^[^@]+@[^@]+$/'],
//     'age' => ['min' => 0, 'max' => 150],
// ]

Includes tests for both populated and empty metadata.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.99%. Comparing base (1db1605) to head (2eabced).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #79      +/-   ##
============================================
+ Coverage     82.93%   82.99%   +0.05%     
- Complexity     1375     1381       +6     
============================================
  Files            40       40              
  Lines          3323     3334      +11     
============================================
+ Hits           2756     2767      +11     
  Misses          567      567              

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