feat(storage): emit per-RPC latency log for put/get handlers

[jacderida]

Summary

Adds a structured info! log event per chunk-store PUT and GET RPC with duration_ms, outcome, and address (and chunk_size on PUT). The tracing target is ant_node::storage::rpc_latency so Elasticsearch / Kibana can build p50/p95/p99 store-RPC latency histograms from the existing telegraf log forwarding without any node-side metric pipeline.

Motivation: a recent testnet (DEV-01) saw aggregate upload throughput halve over 12h before any node failures, with file-size-sensitive degradation that strongly suggests CLOSE_GROUP quorum / slowest-peer-dominates cost on the client. Confirming requires both client-side per-chunk timing (in flight as WithAutonomi/ant-client#87) and node-side per-RPC service time — this PR adds the latter.

Changes

• src/storage/handler.rs: extract the existing handle_put / handle_get bodies into _inner helpers; wrap with Instant::now() and emit a tracing event on every exit path, including the early-return validation paths. Existing per-RPC info!/warn! log lines are kept for human-readable diagnostics.

Test plan

• cargo check --workspace clean
• cargo clippy --workspace --tests clean
• Existing storage handler tests pass
• Spot-check on a dev node that the new event appears in journal output with the expected fields

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds structured per-RPC latency tracing for chunk-store PUT/GET handlers so latency histograms can be built from forwarded logs (without adding a metrics pipeline), by wrapping the existing handler logic and emitting a single info! event with duration_ms, outcome, and chunk address (plus chunk_size on PUT).

Changes:

• Wrapped handle_put/handle_get with timing and a structured info! event targeting ant_node::storage::rpc_latency.
• Extracted the previous PUT/GET logic into handle_put_inner / handle_get_inner so the wrapper can log on all return paths.

Comments suppressed due to low confidence (1)

src/storage/handler.rs:296

• Same as PUT: Instant::now(), hex::encode(...), and duration_ms/outcome are computed regardless of whether the rpc_latency info event will actually be emitted. Please gate this work with crate::logging::enabled! (preferably for this target) and avoid the extra hex-encode in the wrapper (the inner handler already encodes for its debug/warn logs).

        let start = std::time::Instant::now();
        let addr_hex = hex::encode(request.address);
        let response = self.handle_get_inner(request).await;
        let duration_ms = u64::try_from(start.elapsed().as_millis()).unwrap_or(u64::MAX);
        let outcome: &'static str = match &response {

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