Request to change attributes and methods from 'private' to 'protected' in Client.php

[PSF1]

Hello,

While using the PHP client library for Sequra, I encountered the need to extend the Client class to add a custom method for confirming IPN notifications. However, I discovered that all auxiliary attributes and methods in the Client class are declared as private, which prevents their use in any subclass.

I understand that encapsulation is important for maintaining the integrity of the code, but in this case, changing the visibility from private to protected would allow for richer extensibility without compromising the security or internal functioning of the class.

I have implemented these changes in a fork of this repository, which can be found here: https://github.com/frontid/sequra-php-client/tree/master. With these changes, I was able to add the necessary method to efficiently handle IPN notifications.

I believe this change would not only benefit my specific use case but also other developers who may need to extend the library's functionality in the future, while still maintaining the security and stability of the code.

Please consider this change to improve the flexibility and usability of the library.

Thank you for your time and work on this valuable tool.