chore: remove use of async-trait for Rust 1.75.0+

[enmand]

With Rust 1.75.0+, -> impl Trait (including -> impl Future) is supported for Traits, allowing for async trait definitions without the async-trait crate.

Remove use of the async-trait crate, and use Rust's 1.75.0+ features.

https://blog.rust-lang.org/2023/12/21/async-fn-rpit-in-traits.html

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.68%. Comparing base (04afe59) to head (a06afdf).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #92   +/-   ##
=======================================
  Coverage   83.68%   83.68%           
=======================================
  Files           7        7           
  Lines         190      190           
=======================================
  Hits          159      159           
  Misses         31       31           

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