fix: add explicit nullable types to constructor parameters to avoid deprecation notes on PHP 8.4

[alies-dev]

Summary

Fixes PHP 8.4+ deprecation warnings by adding explicit nullable type hints to constructor parameters across Model and API classes.

Problem

The codebase was generating deprecation warnings like:

  PHP Deprecated: OpenAPI\Client\Model\Postcard::__construct(): Implicitly marking parameter $data as nullable is deprecated, the explicit nullable type must be used instead

This occurs because PHP 8.4+ requires explicit nullable type declarations (e.g., ?array $data = null) instead of implicitly nullable parameters (array $data = null).

Solution

• Added explicit nullable type hints (?array, ?Configuration, ?ClientInterface, ?HeaderSelector) to constructor parameters
• Updated corresponding PHPDoc comments to reflect the nullable types
• Maintains backward compatibility while eliminating deprecation warnings

Verify

• [ ] Code runs without errors
• [ ] Tests pass with >=85% line coverage