apollo_starknet_client: drop the feeder call-started log, add latency to the outcome

[matanl-starkware]

What

request_with_retry_url logged twice per feeder HTTP call:

debug!("Call to feeder started. url={url:?}");
let result = ...;
match &result {
    Ok(_)    => debug!("Call to feeder succeeded. url={url:?}"),
    Err(err) => debug!("Call to feeder failed. url={url:?}. Error = {err}"),
}

This drops the "started" line and adds the measured call duration to the outcome line (both the success and the failure branch — failures are where latency matters most, e.g. distinguishing a timeout from an immediate refusal).

Why

Part of a round of log-cost reduction. Measured over 24h of Mainnet logs via Log Analytics, these two lines are the single largest log site on sequencer-core:

site	entries/24h (6 nodes)	% of sequencer-core bytes
reader/mod.rs:214 "Call to feeder started"	2,205,531	5.78%
reader/mod.rs:221 "Call to feeder succeeded"	2,205,483	5.78%

Together 11.56% of the container, ~$240/month across Mainnet + Testnet. That is ~4.25 feeder calls/sec/node, each costing two log entries.

The "started" line carried no information the outcome line doesn't, other than "a call is in flight" — which the new elapsed field conveys, and more usefully.

Follow-up worth considering (not in this PR)

The surviving line still formats the URL with {url:?}, which expands a ~60-character URL into ~400 characters:

url=Url { scheme: "https", cannot_be_a_base: false, username: "", password: None,
          host: Some(Domain("feeder.alpha-mainnet.starknet.io")), port: None,
          path: "/feeder_gateway/get_block", query: Some("blockNumber=latest&..."), fragment: None }

Switching to url.as_str() would save roughly another $60/month for a one-token change. I left it out because it changes the log's shape and wasn't part of the agreed scope — happy to fold it in if reviewers want it.

Test plan

• cargo build -p apollo_starknet_client
• SEED=0 cargo test -p apollo_starknet_client — 76 passed, 0 failed
• scripts/rust_fmt.sh

🤖 Generated with Claude Code

[cursor]

PR Summary

Low Risk
Observability-only change in debug logging; no request, retry, or error-handling behavior changes.

Overview
Cuts feeder gateway debug logging roughly in half by removing the per-request "Call to feeder started" line from request_with_retry_url, leaving a single outcome log per HTTP call.

That outcome log now includes elapsed (via std::time::Instant) on both success and failure paths, so slow or timed-out calls are easier to spot without the extra start entry.

^{Reviewed by Cursor Bugbot for commit 05be00c. Bugbot is set up for automated code reviews on this repo. Configure here.}

[reviewable-StarkWare]

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