Simplify scheduler for compaction/file purge

[v0y4g3r]

What type of enhancement is this?

Refactor

What does the enhancement do?

Currently the Scheduler trait uses an associate type Request,

#[async_trait]
pub trait Scheduler: Debug {
    type Request;

    fn schedule(&self, request: Self::Request) -> Result<bool>;

    async fn stop(&self, await_termination: bool) -> Result<()>;
}

and everytime we add a new scheduler we have to implement all the associate structs like Request/Handler, etc.

This design aims to reduce polymorphic overhead leveraging static dispatching. But this overhead is negligible in this case.
We can use a trait object to simplify the code.

Implementation challenges

No response