Instrument attestation signing. (#8508)

We noticed attestation signing taking 2+ seconds on some of our hoodi nodes and the current traces doesn't provide enough details. This PR adds a few more spans to the `attestation_duty_cycle` code path in the VC.

Before:
<img width="842" height="154" alt="image" src="https://github.com/user-attachments/assets/cfc5c8c0-e6f2-4f56-a8e4-65001af4a005" />

After:
<img width="496" height="217" alt="image" src="https://github.com/user-attachments/assets/c91cfa88-af1b-456e-8c64-625809eb6881" />


  


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

validator_client/signing_method/src/lib.rs

@@ -10,6 +10,7 @@ use reqwest::{Client, header::ACCEPT};
 use std::path::PathBuf;
 use std::sync::Arc;
 use task_executor::TaskExecutor;
+use tracing::instrument;
 use types::*;
 use url::Url;
 use web3signer::{ForkInfo, MessageType, SigningRequest, SigningResponse};
@@ -131,6 +132,7 @@ impl SigningMethod {
     }
 
     /// Return the signature of `signable_message`, with respect to the `signing_context`.
+    #[instrument(skip_all, level = "debug")]
     pub async fn get_signature<E: EthSpec, Payload: AbstractExecPayload<E>>(
         &self,
         signable_message: SignableMessage<'_, E, Payload>,