Function create_engine 

pub fn create_engine(
    entries: u32,
    buffers: Option<&BufferPool>,
    sqpoll: bool,
) -> Result<Box<dyn Engine>>

Creates the best available engine for this system (IO-05 fallback).

Prefers io_uring (when compiled in and permitted — SQPOLL needs a privileged or unbounded user); falls back to mio otherwise.

Errors

Returns the platform error when no engine can be created (io_uring syscall probe fails and mio fallback setup fails).