Migrate tokio and turmoil event loops to use generic version

[camshaft]

Problem:

In #1740, we added a generic event loop implementation to make it easier to maintain all of the current IO providers (and add more in the future). In that PR, I only migrated the io/testing IO provider to improve the focus of the change.

Solution:

All of the IO provider event loops should be using the new generic version. This includes the tokio provider and turmoil provider. This will require implementing the new Rx and Tx traits for the message queue.