Change default to `epoll` and not `io_uring`

## Feature Request

#### Is your feature request related to a problem? Please describe

Currently, when both `epoll` and `io_uring` are part of the classpath the driver would use `io_uring`.

#### Describe the solution you'd like

`io_uring` is still in incubation. It makes more sense to default to `epoll` in such cases.

THIS IS A BREAKING CHANGE.