Accumulator refactor:

Stores a single copy of each request from different sources.
Firewalls identical requests.
Implements time based eviction policy.
Tests.
Like I said above the accumulator acquired a constructor with a default lifetime. After a bit of discussion about it Mahmoud suggested using the Parameters struct. The problem is if we make it a constant we can't test it on short lifetimes and as you noticed below if it gets changed it probably needs reset. So I was thinking about changing it back to an argument with a default value in the Accumulator constructor, are there any objections to that?