This simple module is an RNG-Safe Random Number Sequence. In a nutshell, it is an RNG that you have control over, completely safe from outside Godot RNG calls and reseeding. Now you can simply create an instance of the class with a seed and request items in the sequence, as well as previous results.
This is very useful for procedural generation and testing, where you want a random sequence that is deterministic and protected from outside interference. Since Godot uses a static RNG, it is susceptible to interference and this solves that issue.
This is confirmed to work with Godot 3.0, but should also work with previous and future versions. It is also compatible with in-editor tools! See the repo for more details.