fix: 所有UDP插件添加ReadDeadline防止无限阻塞

SNMP/BACnet/DNS/IPMI/TFTP 的 conn.Read() 在目标不响应时
无限阻塞（goroutine 泄漏），导致整个扫描无法结束。

在 Write 前设置 ReadDeadline 确保超时后返回。

plugins/services/bacnet.go

@@ -34,6 +34,10 @@ func (p *BACnetPlugin) Scan(ctx context.Context, info *common.HostInfo, session
 	}
 	defer conn.Close()
 
+	if dl, ok := conn.(interface{ SetReadDeadline(time.Time) error }); ok {
+		_ = dl.SetReadDeadline(time.Now().Add(timeout))
+	}
+
 	if _, err := conn.Write(bacnetWhoIs); err != nil {
 		return &ScanResult{Success: false, Service: "bacnet"}
 	}

plugins/services/dns.go

@@ -34,6 +34,10 @@ func (p *DNSPlugin) Scan(ctx context.Context, info *common.HostInfo, session *co
 	}
 	defer conn.Close()
 
+	if dl, ok := conn.(interface{ SetReadDeadline(time.Time) error }); ok {
+		_ = dl.SetReadDeadline(time.Now().Add(timeout))
+	}
+
 	if _, err := conn.Write(query); err != nil {
 		return &ScanResult{Success: false, Service: "dns"}
 	}

plugins/services/ipmi.go

@@ -53,6 +53,10 @@ func (p *IPMIPlugin) rmcpPing(ctx context.Context, target string, timeout time.D
 		0x00, // data length = 0
 	}
 
+	if dl, ok := conn.(interface{ SetReadDeadline(time.Time) error }); ok {
+		_ = dl.SetReadDeadline(time.Now().Add(timeout))
+	}
+
 	if _, err := conn.Write(ping); err != nil {
 		return nil
 	}

plugins/services/snmp.go

@@ -75,6 +75,10 @@ func (p *SNMPPlugin) probe(ctx context.Context, target, community string, timeou
 	}
 	defer conn.Close()
 
+	if dl, ok := conn.(interface{ SetReadDeadline(time.Time) error }); ok {
+		_ = dl.SetReadDeadline(time.Now().Add(timeout))
+	}
+
 	pkt := buildSNMPGetRequest(community, []int{1, 3, 6, 1, 2, 1, 1, 1, 0})
 	if _, err := conn.Write(pkt); err != nil {
 		return nil

plugins/services/tftp.go

@@ -33,6 +33,10 @@ func (p *TFTPPlugin) Scan(ctx context.Context, info *common.HostInfo, session *c
 	}
 	defer conn.Close()
 
+	if dl, ok := conn.(interface{ SetReadDeadline(time.Time) error }); ok {
+		_ = dl.SetReadDeadline(time.Now().Add(timeout))
+	}
+
 	if _, err := conn.Write(buildTFTPReadRequest("probe")); err != nil {
 		return &ScanResult{Success: false, Service: "tftp"}
 	}