Random state best practices

[awaelchli]

There are a couple places in the code base where a random state is initialized with

np.random.RandomState(x + y)

The intention here is that a unique state is created for combinations of x and y. However, if different pairs of x and y result in the same sum, there would be a collision. To provide a more distinct and unique seed, we should use a list:

np.random.RandomState([x, y])

Example usages:

https://github.com/Lightning-AI/litdata/blob/a2cfe7bf010bc49c16e34a3c2b6a714ee9acae44/src/litdata/streaming/shuffle.py#L117
https://github.com/Lightning-AI/litdata/blob/a2cfe7bf010bc49c16e34a3c2b6a714ee9acae44/src/litdata/utilities/shuffle.py#L39
https://github.com/Lightning-AI/litdata/blob/a2cfe7bf010bc49c16e34a3c2b6a714ee9acae44/tests/streaming/test_combined.py#L55