Pingora tokio runtime.
Tokio runtime comes in two flavors: a single-threaded runtime
and a multi-threaded one which provides work stealing.
Benchmark shows that, compared to the single-threaded runtime, the multi-threaded one
has some overhead due to its more sophisticated work steal scheduling.
This crate provides a third flavor: a multi-threaded runtime without work stealing.
This flavor is as efficient as the single-threaded runtime while allows the async
program to use multiple cores.