Instrument tracing on block production code path (#8017)

Partially #7814. Instrument block production code path.

New root spans:
* `produce_block_v3`
* `produce_block_v2`

Example traces:

<img width="518" height="432" alt="image" src="https://github.com/user-attachments/assets/a9413d25-501c-49dc-95cc-623db5988981" />


  


Co-Authored-By: Jimmy Chen <jchen.tc@gmail.com>

consensus/fork_choice/src/fork_choice.rs

@@ -523,6 +523,7 @@ where
     ///
     /// You *must* call `get_head` for the proposal slot prior to calling this function and pass
     /// in the result of `get_head` as `canonical_head`.
+    #[instrument(level = "debug", skip_all)]
     pub fn get_proposer_head(
         &self,
         current_slot: Slot,

consensus/state_processing/src/per_slot_processing.rs

@@ -26,7 +26,7 @@ impl From<ArithError> for Error {
 /// If the root of the supplied `state` is known, then it can be passed as `state_root`. If
 /// `state_root` is `None`, the root of `state` will be computed using a cached tree hash.
 /// Providing the `state_root` makes this function several orders of magnitude faster.
-#[instrument(skip_all)]
+#[instrument(level = "debug", skip_all)]
 pub fn per_slot_processing<E: EthSpec>(
     state: &mut BeaconState<E>,
     state_root: Option<Hash256>,