Support __index__() in getrandbits(), randbytes() and others

Feature or enhancement

Support of the __index__() method in getrandbits() and randbytes() is inconsistent.

• Random.getrandbits() supports __index__(), but SystemRandom.getrandbits() does not.
• SystemRandom.randbytes() supports __index__(), but Random.randbytes() does not.

For consistence, both classes should support it.

sample() fails if its k argument is not integer. k should have __index__(), but it also should support comparison with integers and multiplication by list and integer. It is easy to make it more general, and only require __index__(). It will also produce more meaningful error.

binomialvariate() seems "working" with non-integer n argument, but the result is questionable. Passing non-integer value is most likely an error, and it would be better to detect it.

cc @rhettinger

定位 Random.getrandbits()、SystemRandom.getrandbits()、Random.randbytes()、SystemRandom.randbytes()、sample() 和 binomialvariate() 的实现与测试。比较它们对非整数参数的处理方式，然后验证受支持的参数始终一致地使用 index()，并且拒绝无效的 binomialvariate() 输入。