Deprecation Warnings Encountered with PHP 8.1 / Symfony 6.4

[TipPro]

A few deprecation warnings I encountered while running PHP 8.1. Raising this issue to help ensure future compatibility.

Environment:

PHP Version: 8.1
mivaecommerce/api-sdk-php Version: 2.7
Symfony Version: 6.4

Deprecation Notices:

I observed the following deprecation warnings, primarily in the Symfony logs/profiler during application use:

1. Regarding RequestInterface change:
   User Deprecated: The "MerchantAPI\Request::setBinaryEncoding()" method will require a new "?string $encoding" argument in the next major version of its interface "MerchantAPI\RequestInterface", not defining it is deprecated.

2. Regarding JsonSerializable return type in MerchantAPI\Request:
   User Deprecated: Method "JsonSerializable::jsonSerialize()" might add "mixed" as a native return type declaration in the future. Do the same in implementation "MerchantAPI\Request" now to avoid errors or add an explicit @return annotation to suppress this message.

3. Regarding JsonSerializable return type in MerchantAPI\Model:
   User Deprecated: Method "JsonSerializable::jsonSerialize()" might add "mixed" as a native return type declaration in the future. Do the same in implementation "MerchantAPI\Model" now to avoid errors or add an explicit @return annotation to suppress this message.

[ghassani]

I have not yet looked into this but we should get around to dropping support for any older versions of PHP that may be causing this in the next release.