feat(o11y): Attach tracing context to messages received by PeerManagerActor

[nikurt]

This PR complete tracing of async work across all actix Actors.
https://pagodaplatform.atlassian.net/browse/ND-171

[nagisa]

Instead of duplicating the macro body, consider making handler_span able to take a parameter that describes level (and invokes tracing::span!) and then add handler_debug_span/handler_trace_span helpers.

The matcher will likely look a lot like this:

macro_rules! handler_span {
    (target: $target:expr, $lvl:expr, $msg:expr, $($extra_fields:tt)*) => {{
        let WithSpanContext { msg, context, .. } = $msg;
        let span = $crate::tracing::span!(
            target: $target,
            $lvl,
            "handle",
            handler = $crate::macros::type_name_of(&msg),
            actor = $crate::macros::last_component_of_name(std::any::type_name::<Self>()),
            $($extra_fields)*)
        .entered();
        span.set_parent(context);
        (span, msg)
    }}
}

macro_rules! handler_trace_span {
    ($target:expr, $msg:expr, $($extra_fields:tt)*) => {
        $crate::handler_span!(target: $target, $crate::tracing::Level::TRACE, $msg, $($extra_fields)*
    }
}

I see a couple issues I didn’t spot last time too:

1. it is worth it to keep actor and handler expressions within the span! macro, as this way they will end up within the if ... {} condition that decides whether the span is enabled at all, and will be guaranteed to not be processed if the span is disabled;
2. The extra_fields tt matcher should not be separated by commas, I think. It prevents passing through valid token forests such as foo = expression() etc.

[nikurt]

Followed the approach from https://docs.rs/tracing/latest/src/tracing/macros.rs.html#24 .
Tested that handler_trace_span! can be called with repeated extra fields, including a = 2+3 fields.

[nagisa]

Looks great!