feat: Add a method to get the current state of `Random\Engine\PcgOneseq128XslRr64` engine

[Crovitche-1623]

Description

Actually a jump method is available to moves the algorithm’s state ahead by the number of steps given by advance. However, there are no built-in method to retrieve the current state of the algorithm.

This force to keep a class that decorates this engine to save the state of the algorithm although the state is known internally (I imagine) if we want to restore the state later (e.g. when creating a new engine).

It would be a good improvement to have a getState() method that returns the number of steps the algorithm has already advanced.

[Crovitche-1623]

E.g. Python has a method to do this: https://docs.python.org/3/library/random.html#random.getstate

[TimWolla]

All the engines (except Secure) support serialization:

<?php

var_dump(serialize(new \Random\Engine\PcgOneseq128XslRr64(0)));

results in:

string(121) "O:33:"Random\Engine\PcgOneseq128XslRr64":2:{i:0;a:0:{}i:1;a:2:{i:0;s:16:"f8734299c9be7148";i:1;s:16:"9a4583381c8a1fac";}}"

[Crovitche-1623]

Thanks @TimWolla.

In other words if the engine needs to be restored later, you think it's more reliable to store the serialized engine and retrieve it later using deserialization than storing the state property? The only drawback I can see is that it would be less interoperable with other systems if only the state (with its seed in certain cases too) is needed to rebuild the engine.

[TimWolla]

Serialization is the intended solution to serialize the engine state, yes.

Interoperability is not really a thing either way, since the functions to turn the engine output into, say, an integer (Randomizer::getInt()) will differ between different programming languages. The raw engine output is not all that interesting by itself.

[Crovitche-1623]

Okay, the result won't be the same if the implementation isn't exactly the same from what I understand. That makes sense now thanks for your help.