Create an Exponential Distribution

## Why its important to make this change
Once the abstraction of replacing the RNG with a Distribution object has been completed, there should be an implementation of Exponential give that its a standard function.

## How much time I would invest in making this patch (if I had the free time to do it)
3 hours

First locate the Distribution abstraction mentioned in the issue and inspect any existing distribution implementations. Add the Exponential distribution in the same area, then verify its standard behavior with the project's existing tests or test pattern; the issue names no specific files or test entry point.

Written by the indexing model from the issue text.