Use tokio tasks

[Milo123459]

Uses tokio tasks instead of std::thread::spawn

[zakajd]

gives a ~1.5% improvements on a server with 16 cores / 32 threads

[HardhatChad]

Reviewing now. How many samples did you take to measure 1.5% improvement? There's a lot of noise in the benchmark as it can vary a lot from one run to the next

[Milo123459]

Well, this will just improve scheduling. Thanks to the parallel starting of the tasks, it will be a little bit faster. I can update this PR if you'd like to fix conflicts?