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/genericopt.go

@@ -0,0 +1,56 @@
+// 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
+
+// TrafficClass returns the traffic class field value for outgoing
+// packets.
+func (c *genericOpt) TrafficClass() (int, error) {
+	if !c.ok() {
+		return 0, errInvalidConn
+	}
+	so, ok := sockOpts[ssoTrafficClass]
+	if !ok {
+		return 0, errNotImplemented
+	}
+	return so.GetInt(c.Conn)
+}
+
+// SetTrafficClass sets the traffic class field value for future
+// outgoing packets.
+func (c *genericOpt) SetTrafficClass(tclass int) error {
+	if !c.ok() {
+		return errInvalidConn
+	}
+	so, ok := sockOpts[ssoTrafficClass]
+	if !ok {
+		return errNotImplemented
+	}
+	return so.SetInt(c.Conn, tclass)
+}
+
+// HopLimit returns the hop limit field value for outgoing packets.
+func (c *genericOpt) HopLimit() (int, error) {
+	if !c.ok() {
+		return 0, errInvalidConn
+	}
+	so, ok := sockOpts[ssoHopLimit]
+	if !ok {
+		return 0, errNotImplemented
+	}
+	return so.GetInt(c.Conn)
+}
+
+// SetHopLimit sets the hop limit field value for future outgoing
+// packets.
+func (c *genericOpt) SetHopLimit(hoplim int) error {
+	if !c.ok() {
+		return errInvalidConn
+	}
+	so, ok := sockOpts[ssoHopLimit]
+	if !ok {
+		return errNotImplemented
+	}
+	return so.SetInt(c.Conn, hoplim)
+}