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_unix.go

@@ -0,0 +1,40 @@
+//go:build !linux && !windows
+// +build !linux,!windows
+
+// only tested on OSX
+// decided to go with exec.Command after I couldn't figure
+// out how to extract the arp cache out of the kernel with
+// golang's syscall or Sysctl()
+//
+// ... Help appreciated :)
+
+package arp
+
+import (
+	"os/exec"
+	"strings"
+)
+
+// Table 通过 arp -an 命令读取 ARP 表（类 Unix 平台，仅在 OSX 测试过）
+func Table() ArpTable {
+	data, err := exec.Command("arp", "-an").Output()
+	if err != nil {
+		return nil
+	}
+
+	var table = make(ArpTable)
+	for _, line := range strings.Split(string(data), "\n") {
+		fields := strings.Fields(line)
+		if len(fields) < 3 {
+			continue
+		}
+
+		// strip brackets around IP
+		ip := strings.Replace(fields[1], "(", "", -1)
+		ip = strings.Replace(ip, ")", "", -1)
+
+		table[ip] = fields[3]
+	}
+
+	return table
+}