Fix long overflow by specifying getting state upto Instant.now()

[faraway]

I found this few weeks back when I was doing something similar to the concursus-spring-boot-demo app. Then I saw someone has the same problem as reported in issue #17

The problem is quite straightforward, when we call groupStateRepository.getStates(groups) in test code, it in turn calls getState(groups, Instant.MAX), where Instant.MAX is the upper bound. Later on when in CassandraEventRetriever.constrainBound, it calls bound.getInstant().toEpochMilli()) which results in the long overflow exception.
The problem can be simply reproduced by Instant.MAX.toEpochMilli())

Anyways, I'm not sure if Instant.MAX is intended. From the code comments, it seems to be Instant.now(), which translates to "get the events up to now". whereas Instant.MAX means to the far future based on its own documentation.

At the meantime, a simple workaround (as currently what i'm doing) is to specify the upper bound (i.e. do groupStateRepository.getStates(groups, Instant.now()) instead). The error goes away

[poetix]

Thanks very much for this! It's surprising (to me) that Instant can encode a time value that isn't expressible in long millis-since-epoch; also surprising that I hadn't noticed this issue myself...