feat(arp): 自 go-hua 迁入 ARP 表查询与定时刷新缓存

- IP→MAC 查询(AutoRefresh 后台刷新/Search/Table), 新增依赖 mostlygeek/arp
- 附测试、examples/arp 例程与包 README

arp/arp_linux.go

@@ -0,0 +1,43 @@
+//go:build linux
+// +build linux
+
+package arp
+
+import (
+	"bufio"
+	"os"
+	"strings"
+)
+
+const (
+	f_IPAddr int = iota
+	f_HWType
+	f_Flags
+	f_HWAddr
+	f_Mask
+	f_Device
+)
+
+// Table 读取 Linux 内核 ARP 表（/proc/net/arp）
+func Table() ArpTable {
+	f, err := os.Open("/proc/net/arp")
+
+	if err != nil {
+		return nil
+	}
+
+	defer f.Close()
+
+	s := bufio.NewScanner(f)
+	s.Scan() // skip the field descriptions
+
+	var table = make(ArpTable)
+
+	for s.Scan() {
+		line := s.Text()
+		fields := strings.Fields(line)
+		table[fields[f_IPAddr]] = fields[f_HWAddr]
+	}
+
+	return table
+}