chore: replace futures::mpsc with tokio::mpsc for Axum compatibility

[mdqst]

I replaced futures::mpsc::UnboundedSender with tokio::sync::mpsc::UnboundedSender in the Axum server setup. The original sender doesn't implement Sync, which causes issues when used with axum::extract::State.

tokio::mpsc::UnboundedSender implements Clone + Send + Sync + 'static, making it a better fit here and removing the need to wrap the sender in Arc<Mutex<...>>. The fix makes the enqueue route work as intended without extra boilerplate.

[vercel]

@mdqst is attempting to deploy a commit to the unionbuild Team on Vercel.

A member of the Team first needs to authorize it.

[benluelo]

thanks for the PR! was there an issue with the current design that this PR fixes? you mention Arc<Mutex<...>>, but we don't use that anywhere in the router.

[mdqst]

Thanks for the feedback, benluelo! I encountered an issue when trying to use futures::mpsc::UnboundedSender with axum::extract::State, since the original sender does not implement Sync, which caused problems when working with multiple threads. Switching to tokio::sync::mpsc::UnboundedSender resolves this issue because it implements Sync, removing the need to wrap the sender in Arc<Mutex<...>>, as would be required with futures::mpsc. This change helps avoid potential concurrency issues and simplifies the code without introducing extra boilerplate.

[benluelo]

I'm still not sure what problem you're trying to solve? The code works as it is right now.