Investigate making the timers API similar to the `futures-native-timers` crate

[fitzgen]

https://github.com/tinaun/futures-native-timers

As similar as it could be within reason. This would enable building a cross-platform (native and wasm) timers crate without too much hassle. This would bring good cross-ecosystem pollination and do a tiny amount of work towards transparent server-side/client-side style applications.