Change fn visibility to reduce MSRV from 1.74 to 1.66

[fornwall]

Thanks a lot for publishing 0.9.0!

That version has an issue that makes it require rust 1.74 - on earlier versions the build fails with:

error[E0446]: crate-private type EventFd in public interface
--> src/run.rs:49:1
|
31 | pub(crate) struct EventFd(pub(crate) Arc);
| ------------------------- EventFd declared as crate-private
...
49 | pub fn run(context: Arc, setmap: SetMap, max_length: usize, receiver: Receiver, evt_fd: EventFd) {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can't leak crate-private type

This PR lowers the MSRV to 1.66 (where std::os::fd was introduced) - if possible it would be nice with a 0.9.1 including it!

[quininer]

Thank you!

[fornwall]

Thanks yourself for the speedy 0.9.1 release!