Random number generator tests
We need to strengthen the unit test of the random number generator. This includes:
- Make sure two adjacent IDs do not get correlated numbers at a fixed ti_current
- Make sure a given ID does not get correlated outputs at subsequent ti_current
- Make sure two IDs from a given galaxy (e.g. from the actual EAGLE 25) are not correlated at a fixed ti_current.
The first two of these can be easily built into the current unit test. And verify that the test actually passes under these conditions.