Remove dependencies

[pedrorrivero]

Is your feature request related to a problem? Please describe.

As of May 2021, QRAND depends on NumPy and randomgen, but it only needs certain parts of these packages. Particularly, it only needs a number of data types (float64, uint32, uint64) from the former, and the UserBitGenerator class from the latter.

Describe the solution you'd like

Removing this dependencies would make QRAND faster, lighter, and less fragile. We would need:

• Data-type stubs for NumPy. These should not change very often and so they will be easy to maintain.
• An interface equivalent to UserBitGenerator that can be implemented by QuantumBitGenerator.

Describe alternatives you've considered

Apparently, randomgen is slowly merging into NumPy, so maybe in some time from now we will be able to naturally reduce the dependencies to only the latter with no additional effort. Nonetheless, NumPy is a rather large library and we would only make use of a very limited portion of it.

Additional context

The randomgen package depends on NumPy itself, so it would be necessary to assess wether this dependency could be entirely removed.

Even if impractical, removing the explicit NumPy dependency would help mitigating conflicts. Luckily, this should be easy to do. A possible solution would be building data-type stubs through Python's own ctypes.

Regardless of the above, since QRAND is meant to be able to interface with NumPy we would still need to keep it as an extra dependency.