Support for Rand 0.9

Rand updated their APIs in 0.9: https://github.com/rust-random/rand/releases/tag/0.9.0. We should update our APIs accordingly so that it is easy for users to upgrade their Rand dependency (or use Shuttle with a project which uses Rand 0.9). I think the easiest might be to offer both the 0.9 and the 0.8 API. One alternative is to "cratify" this functionality; have a ShuttleRand crate at version 0.8, and a ShuttleRand crate 0.9, and then let users import accordingly.

Start with the Rand 0.9 release notes linked in the issue and compare the current Shuttle Rand API with the affected Rand 0.8 usage. Decide whether compatibility belongs in one API or separate ShuttleRand crate versions, then verify that a Shuttle project can use Rand 0.9 while retaining the required behavior.

Written by the indexing model from the issue text.