Instrument tracing spans for block processing and import (#7816)

#7815

- removes all existing spans, so some span fields that appear in logs like `service_name` may be lost.
- instruments a few key code paths in the beacon node, starting from **root spans** named below:

* Gossip block and blobs
* `process_gossip_data_column_sidecar`
* `process_gossip_blob`
* `process_gossip_block`
* Rpc block and blobs
* `process_rpc_block`
* `process_rpc_blobs`
* `process_rpc_custody_columns`
* Rpc blocks (range and backfill)
* `process_chain_segment`
* `PendingComponents` lifecycle
* `pending_components`

To test locally:
* Run Grafana and Tempo with https://github.com/sigp/lighthouse-metrics/pull/57
* Run Lighthouse BN with `--telemetry-collector-url http://localhost:4317`

Some captured traces can be found here: https://hackmd.io/@jimmygchen/r1sLOxPPeg

Removing the old spans seem to have reduced the memory usage quite a lot - i think we were using them on long running tasks and too excessively:
<img width="910" height="495" alt="image" src="https://github.com/user-attachments/assets/5208bbe4-53b2-4ead-bc71-0b782c788669" />

beacon_node/beacon_chain/src/canonical_head.rs

@@ -55,7 +55,7 @@ use std::sync::Arc;
 use std::time::Duration;
 use store::{iter::StateRootsIterator, KeyValueStore, KeyValueStoreOp, StoreItem};
 use task_executor::{JoinHandle, ShutdownReason};
-use tracing::{debug, error, info, warn};
+use tracing::{debug, error, info, instrument, warn};
 use types::*;
 
 /// Simple wrapper around `RwLock` that uses private visibility to prevent any other modules from
@@ -471,6 +471,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
     /// Execute the fork choice algorithm and enthrone the result as the canonical head.
     ///
     /// This method replaces the old `BeaconChain::fork_choice` method.
+    #[instrument(skip_all, level = "debug")]
     pub async fn recompute_head_at_current_slot(self: &Arc<Self>) {
         match self.slot() {
             Ok(current_slot) => self.recompute_head_at_slot(current_slot).await,