fix: vendor deps and fix CI go-version, timeout, GOTOOLCHAIN (HAN-414)

- Run go mod vendor to eliminate proxy.golang.org network dependency
- Set GOFLAGS=-mod=vendor at job env level so all go commands use vendor/
- Fix go-version from 1.23 to 1.24.0 to match go.mod
- Move GOTOOLCHAIN=local to job-level env (not per-step inline)
- Set cache: false on setup-go (cache is irrelevant with vendoring)
- Add timeout-minutes: 15 so failures are caught quickly instead of 3h

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: multica-agent <github@multica.ai>

vendor/golang.org/x/net/ipv6/helper.go

@@ -0,0 +1,58 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ipv6
+
+import (
+	"errors"
+	"net"
+	"runtime"
+)
+
+var (
+	errInvalidConn     = errors.New("invalid connection")
+	errMissingAddress  = errors.New("missing address")
+	errHeaderTooShort  = errors.New("header too short")
+	errInvalidConnType = errors.New("invalid conn type")
+	errNotImplemented  = errors.New("not implemented on " + runtime.GOOS + "/" + runtime.GOARCH)
+)
+
+func boolint(b bool) int {
+	if b {
+		return 1
+	}
+	return 0
+}
+
+func netAddrToIP16(a net.Addr) net.IP {
+	switch v := a.(type) {
+	case *net.UDPAddr:
+		if ip := v.IP.To16(); ip != nil && ip.To4() == nil {
+			return ip
+		}
+	case *net.IPAddr:
+		if ip := v.IP.To16(); ip != nil && ip.To4() == nil {
+			return ip
+		}
+	}
+	return nil
+}
+
+func opAddr(a net.Addr) net.Addr {
+	switch a.(type) {
+	case *net.TCPAddr:
+		if a == nil {
+			return nil
+		}
+	case *net.UDPAddr:
+		if a == nil {
+			return nil
+		}
+	case *net.IPAddr:
+		if a == nil {
+			return nil
+		}
+	}
+	return a
+}