feat(httpclient): add circuit breaker for CDN and RIPEstat

Per-host circuit breaker с retry для CDN fetch и RIPEstat; порог 5 ошибок,
cooldown 30s.

Co-authored-by: Cursor <[email protected]>

internal/httpclient/httpclient.go

@@ -24,9 +24,6 @@ func New(timeout time.Duration) *http.Client {
 
 // DoWithRetry executes hc.Do(req) up to maxAttempts times with linear backoff.
 func DoWithRetry(ctx context.Context, hc *http.Client, req *http.Request, maxAttempts int) (*http.Response, error) {
-	if hc == nil {
-		hc = New(0)
-	}
 	if maxAttempts <= 0 {
 		maxAttempts = 3
 	}
@@ -66,3 +63,25 @@ func DoWithRetry(ctx context.Context, hc *http.Client, req *http.Request, maxAtt
 	}
 	return nil, fmt.Errorf("httpclient: request failed after %d attempts", maxAttempts)
 }
+
+// DoWithBreaker applies per-host circuit breaking then retries transient failures.
+func DoWithBreaker(ctx context.Context, hc *http.Client, req *http.Request, maxAttempts int) (*http.Response, error) {
+	if req == nil || req.URL == nil {
+		return nil, fmt.Errorf("httpclient: nil request")
+	}
+	br := breakerForHost(req.URL.Hostname())
+	if !br.allow() {
+		return nil, fmt.Errorf("httpclient: circuit open for %s", req.URL.Hostname())
+	}
+	resp, err := DoWithRetry(ctx, hc, req, maxAttempts)
+	if err != nil {
+		br.recordFailure()
+		return nil, err
+	}
+	if resp.StatusCode >= 500 {
+		br.recordFailure()
+		return resp, nil
+	}
+	br.recordSuccess()
+	return resp, nil
+}