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/pipeline/upstream_http.go

@@ -0,0 +1,23 @@
+package pipeline
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+
+	"evobgp/internal/httpclient"
+)
+
+func upstreamHTTPDo(ctx context.Context, hc *http.Client, req *http.Request) (*http.Response, error) {
+	if hc == nil {
+		hc = httpclient.New(httpclient.DefaultTimeout)
+	}
+	resp, err := httpclient.DoWithBreaker(ctx, hc, req, 3)
+	if err != nil {
+		if req.URL != nil {
+			return nil, fmt.Errorf("cdn fetch %s: %w", req.URL.String(), err)
+		}
+		return nil, err
+	}
+	return resp, nil
+}