Modularize tracing executor and metrics rename (#6424)

* Tracing executor and metrics rename

* Appease clippy

* Merge branch 'unstable' into modularise-task-executor

common/slot_clock/src/metrics.rs

@@ -1,5 +1,5 @@
 use crate::SlotClock;
-pub use lighthouse_metrics::*;
+pub use metrics::*;
 use std::sync::LazyLock;
 use types::{EthSpec, Slot};