Callback type of `Client::register` and `Client::subscribe` produces lifetime issues in closures

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Callback type of `Client::register` and `Client::subscribe` produces lifetime issues in closures

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83325d9 is implementing one of the proposed methods but leads to a nearly unusable API (see commit message).

I had a deep look into lifetimes and callbacks while trying to implement this and figured out that the existing implementation works fine when moving the variable holding the context that is needed for the callback into the callback (transfering ownership).

impl A {
    pub fn run(self) {
        // ...
        let ctx = self.data;
        client.register(uri, Box::new(move |args, kwargs| Self::authenticate(&ctx, args, kwargs)));
        // ... self is used here
    }
}

This makes self.data inaccessible after the register call but this is intended behavior.

I'm still learning rust so sorry for the misleading input 😅

I will close this issue as the callback types are correct!