feat: emit errors in prover API metrics (#2890)

## What ❔

Report reasons of failed calls in prover API metrics.

## Why ❔

To have more observability

## Checklist

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- [ ] PR title corresponds to the body of PR (we generate changelog
entries from PRs).
- [ ] Tests for the changes have been added / updated.
- [ ] Documentation comments have been added / updated.
- [ ] Code has been formatted via `zk fmt` and `zk lint`.

core/node/external_proof_integration_api/src/lib.rs

@@ -19,10 +19,7 @@ use types::{ExternalProof, ProofGenerationDataResponse};
 use zksync_basic_types::L1BatchNumber;
 
 pub use crate::processor::Processor;
-use crate::{
-    metrics::{CallOutcome, Method},
-    middleware::MetricsMiddleware,
-};
+use crate::{metrics::Method, middleware::MetricsMiddleware};
 
 /// External API implementation.
 #[derive(Debug)]
@@ -37,11 +34,7 @@ impl Api {
             axum::middleware::from_fn(move |req: Request, next: Next| async move {
                 let middleware = MetricsMiddleware::new(method);
                 let response = next.run(req).await;
-                let outcome = match response.status().is_success() {
-                    true => CallOutcome::Success,
-                    false => CallOutcome::Failure,
-                };
-                middleware.observe(outcome);
+                middleware.observe(response.status());
                 response
             })
         };

core/node/external_proof_integration_api/src/metrics.rs

@@ -2,13 +2,6 @@ use std::time::Duration;
 
 use vise::{EncodeLabelSet, EncodeLabelValue, Histogram, LabeledFamily, Metrics};
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, EncodeLabelSet, EncodeLabelValue)]
-#[metrics(label = "outcome", rename_all = "snake_case")]
-pub(crate) enum CallOutcome {
-    Success,
-    Failure,
-}
-
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, EncodeLabelSet, EncodeLabelValue)]
 #[metrics(label = "type", rename_all = "snake_case")]
 pub(crate) enum Method {
@@ -20,8 +13,8 @@ pub(crate) enum Method {
 #[derive(Debug, Metrics)]
 #[metrics(prefix = "external_proof_integration_api")]
 pub(crate) struct ProofIntegrationApiMetrics {
-    #[metrics(labels = ["method", "outcome"], buckets = vise::Buckets::LATENCIES)]
-    pub call_latency: LabeledFamily<(Method, CallOutcome), Histogram<Duration>, 2>,
+    #[metrics(labels = ["method", "status"], buckets = vise::Buckets::LATENCIES)]
+    pub call_latency: LabeledFamily<(Method, u16), Histogram<Duration>, 2>,
 }
 
 #[vise::register]

core/node/external_proof_integration_api/src/middleware.rs

@@ -1,6 +1,7 @@
+use axum::http::StatusCode;
 use tokio::time::Instant;
 
-use crate::metrics::{CallOutcome, Method, METRICS};
+use crate::metrics::{Method, METRICS};
 
 #[derive(Debug)]
 pub(crate) struct MetricsMiddleware {
@@ -16,7 +17,8 @@ impl MetricsMiddleware {
         }
     }
 
-    pub fn observe(&self, outcome: CallOutcome) {
-        METRICS.call_latency[&(self.method, outcome)].observe(self.started_at.elapsed());
+    pub fn observe(&self, status_code: StatusCode) {
+        METRICS.call_latency[&(self.method, status_code.as_u16())]
+            .observe(self.started_at.elapsed());
     }
 }