Move to numpy random generator decorator

[CharJon]

Currently we are using the networkx decorator for randomness.
The design is tailored to not require numpy, but as we build on numpy anyways, we could write our own decorator.
Possible benefits:

• Easier to understand decorator, as we can keep the code way more compact than numpys implementation
• Better performance and more functions, as e.g. arrays of random elements can be created at once.

Link to numpy random generators.