Use dynamic dispatch to simplify reporters

[charliermarsh]

Summary

Sort of undecided on this. These are already stored as dyn Reporter in each struct, so we're already using dynamic dispatch in that sense. But all the methods take impl Reporter. This is sometimes nice (the callsites are simpler?), but it also means that in practice, you often can't pass None to these methods that accept Option<impl Reporter>, because Rust can't infer the generic type.

Anyway, this adds more consistency and simplifies the setup by using Arc<dyn Reporter> everywhere.

[charliermarsh]

I'm really annoyed by this whole Facade setup... I want to be able to do something like:

impl <T: Reporter> uv_distribution::Reporter for Arc<dyn T> {
    fn on_build_start(&self, source: &BuildableSource) -> usize {
        self.on_build_start(source)
    }

    fn on_build_complete(&self, source: &BuildableSource, id: usize) {
        self.on_build_complete(source, id);
    }

    fn on_checkout_start(&self, url: &Url, rev: &str) -> usize {
        self.on_checkout_start(url, rev)
    }

    fn on_checkout_complete(&self, url: &Url, rev: &str, id: usize) {
        self.on_checkout_complete(url, rev, id);
    }
}

But I run into orphan trait problems.

The general problem here is that I have multiple Reporter traits. And if you implement one of them, then you should get some others "for free". But for now, I have to do this:

/// A facade for converting from [`Reporter`] to [`uv_git::Reporter`].
pub(crate) struct Facade {
    reporter: Arc<dyn Reporter>,
}

impl From<Arc<dyn Reporter>> for Facade {
    fn from(reporter: Arc<dyn Reporter>) -> Self {
        Self { reporter }
    }
}

impl uv_git::Reporter for Facade {
    fn on_checkout_start(&self, url: &Url, rev: &str) -> usize {
        self.reporter.on_checkout_start(url, rev)
    }

    fn on_checkout_complete(&self, url: &Url, rev: &str, id: usize) {
        self.reporter.on_checkout_complete(url, rev, id);
    }
}