Deprecated return type for function offsetGet

[sebasparola]

Describe the bug
For newer versions of PHP (>=8.1) the offsetGet functionality is giving deprecation warnings

To Reproduce
Create a new Entity

Expected behavior
No warning or Error

Additional context

[sebasparola]

Two possible solutions that I have tested and worked fine for this were:

1. add the return type mixed for the function in the Entity class:
   public function offsetGet( $offset ) : mixed {

or

2. add the overrride #[\ReturnTypeWillChange] annotation to the offsetGet function

[mrudov]

Fixed in v4 branch. Please refer README.md for details.