Migrate from `async-trait` to native (Rust 1.75)

[LeoBorai]

Thanks to Rust 1.75, we can now make use of async fn in traits (with certain limitations).

Read more here: https://blog.rust-lang.org/2023/12/28/Rust-1.75.0.html#async-fn-and-return-position-impl-trait-in-traits

A PR testing what can be changed would be awesome, to start making progress on this side.

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