refactor codebase and fix bugs

- merge dante.go and dante_control.go into single dante.go
- consolidate buildDantePacket and buildDantePacket28 into one function
- fix broken comparison logic in SetDanteClockMaster
- split ARP parsing into platform-specific files with build tags
- implement Linux ARP table parsing via /proc/net/arp
- run gofmt on all files

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

arp_darwin.go

@@ -0,0 +1,62 @@
+//go:build darwin
+
+package tendrils
+
+import (
+	"bufio"
+	"log"
+	"net"
+	"os/exec"
+	"strings"
+)
+
+func (t *Tendrils) parseARPTable() []arpEntry {
+	cmd := exec.Command("arp", "-an")
+	output, err := cmd.Output()
+	if err != nil {
+		return nil
+	}
+
+	var entries []arpEntry
+	scanner := bufio.NewScanner(strings.NewReader(string(output)))
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		if strings.Contains(line, "permanent") {
+			continue
+		}
+
+		fields := strings.Fields(line)
+		if len(fields) < 6 {
+			continue
+		}
+
+		ipStr := strings.Trim(fields[1], "()")
+		ip := net.ParseIP(ipStr)
+		if ip == nil {
+			continue
+		}
+
+		macStr := fields[3]
+		if macStr == "(incomplete)" {
+			continue
+		}
+
+		macStr = normalizeMACAddress(macStr)
+		mac, err := net.ParseMAC(macStr)
+		if err != nil {
+			log.Printf("[arp] failed to parse MAC %q for IP %s: %v", macStr, ipStr, err)
+			continue
+		}
+
+		ifaceName := fields[5]
+
+		entries = append(entries, arpEntry{
+			ip:    ip,
+			mac:   mac,
+			iface: ifaceName,
+		})
+	}
+
+	return entries
+}