Lightweight actor library inspired by actix and xactor.
See tests/integration_test.rs for usage example.
The lifecycle of Addr<T> of other actor frameworks is equivalent to Arc<T>, which doesn't work well with RAII.
flo-state distinguishes between Owner<T> and Addr<T>, and when Owner<T> is dropped, all related Addr<T>s and the associated spawned tasks are cancelled deterministically.