Make task executor configurable

[bltavares]

Currently, this libraries since #21 has been using async-std to spawn new tasks.

We could instead offer the task executor to be configurable using cargo feature selectors. There is the https://github.com/bastion-rs/agnostik crate to help with this.

This would let the code to be also used on Tokio or Bastions codebases (preferring using async-std or smol by default, given that we still make use of async-std::RwLock on other stuff.

I have no idea what a proactive IO framework is as well - but it would be worth checking if it make sense to use (https://github.com/vertexclique/nuclei)

Given that colmeia-hyperswarm-mdns crate is using my own custon multicast-socket crate, it would not benefit from async-std's epoll io or bastion-rs/nuclei. The replicator crate would be the next one that need to find a good io replicator.

TODO on a livestream:

• [ ] Include bastions-rs/agnostik crate on every crate that spawns tasks
• [ ] Add feature selector to select which crate to use

Investigation:

• https://github.com/bastion-rs/agnostik
• https://github.com/vertexclique/nuclei
• https://crates.io/crates/multitask
• https://crates.io/crates/async-task
• An alternative to async-std::sync::RwLock so we can leave it as an optional dependency - https://crates.io/crates/async-rwlock https://crates.io/crates/futures-locks

[bltavares]

https://crates.io/crates/async_executors

[bltavares]

https://crates.io/crates/async-rwlock

[bltavares]

https://crates.io/crates/async-executor/