fix(httpclient): replace DefaultClient with timed clients and retry

Пакет httpclient: timeout 45s, idle pool, DoWithRetry. Scheduler и nodecli
используют retry; pipeline/asnresolve/jobs — httpclient.New вместо DefaultClient.

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

internal/httpclient/httpclient.go

@@ -0,0 +1,68 @@
+// Package httpclient provides shared HTTP clients and retry helpers for outbound calls.
+package httpclient
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+)
+
+const DefaultTimeout = 45 * time.Second
+
+// New returns an HTTP client with timeout and tuned idle connection pooling.
+func New(timeout time.Duration) *http.Client {
+	if timeout <= 0 {
+		timeout = DefaultTimeout
+	}
+	tr := http.DefaultTransport.(*http.Transport).Clone()
+	tr.MaxIdleConns = 100
+	tr.MaxIdleConnsPerHost = 10
+	return &http.Client{Timeout: timeout, Transport: tr}
+}
+
+// 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
+	}
+	var lastErr error
+	for attempt := 0; attempt < maxAttempts; attempt++ {
+		if attempt > 0 {
+			wait := time.Duration(attempt) * 2 * time.Second
+			select {
+			case <-ctx.Done():
+				return nil, ctx.Err()
+			case <-time.After(wait):
+			}
+			if req.GetBody != nil {
+				body, err := req.GetBody()
+				if err != nil {
+					return nil, err
+				}
+				req.Body = body
+			}
+		}
+		reqClone := req.Clone(ctx)
+		resp, err := hc.Do(reqClone)
+		if err != nil {
+			lastErr = err
+			continue
+		}
+		if resp.StatusCode >= 500 {
+			_, _ = io.Copy(io.Discard, resp.Body)
+			_ = resp.Body.Close()
+			lastErr = fmt.Errorf("httpclient: upstream %s", resp.Status)
+			continue
+		}
+		return resp, nil
+	}
+	if lastErr != nil {
+		return nil, lastErr
+	}
+	return nil, fmt.Errorf("httpclient: request failed after %d attempts", maxAttempts)
+}