feat(bytepacket): 自 go-hua 迁入二进制封包工具

- 小端序读写, 兼容易语言协议(GBK 字符串/易语言日期)
- 附测试、examples/bytepacket 例程与包 README

examples/bytepacket/main.go

@@ -0,0 +1,43 @@
+// bytepacket 包示例：二进制封包/解包（小端序，兼容易语言协议，含 GBK 字符串与易语言日期）
+package main
+
+import (
+	"fmt"
+
+	"git.zeroonesoft.cn/golib/zogo/bytepacket"
+)
+
+func main() {
+	// ===== 写入封包 =====
+	p := bytepacket.NewPacket(nil)
+	p.WriteInt32(100)
+	p.WriteUInt16(200)
+	_ = p.WriteString("hello")
+	_ = p.WriteStringGbk("中文GBK")
+	_ = p.WriteBytes([]byte{1, 2, 3})
+
+	data := p.GetData()
+	fmt.Printf("封包总长: %d 字节\n", len(data))
+
+	// ===== 读取封包（按写入顺序读出）=====
+	r := bytepacket.NewPacket(data)
+	fmt.Println("ReadInt32:", r.ReadInt32())
+	fmt.Println("ReadUInt16:", r.ReadUInt16())
+	s, _ := r.ReadString()
+	fmt.Println("ReadString:", s)
+	gbk, _ := r.ReadStringGbk()
+	fmt.Println("ReadStringGbk:", gbk)
+	fmt.Println("ReadBytes:", r.ReadBytes())
+
+	// ===== GBK / UTF-8 互转 =====
+	gbkBytes, _ := bytepacket.Utf8ToGbk([]byte("编码转换"))
+	fmt.Printf("UTF-8→GBK: % X\n", gbkBytes)
+	utf8Bytes, _ := bytepacket.GbkToUtf8(gbkBytes)
+	fmt.Println("GBK→UTF-8:", string(utf8Bytes))
+
+	// ===== 易语言日期时间（float64 天数，起点 1899-12-30）=====
+	d := bytepacket.NewPacket(nil)
+	d.WriteFloat64(45292.5) // ≈ 2024-01-01 12:00:00
+	t := d.ReadElangDateTime()
+	fmt.Println("ReadElangDateTime:", t.Format("2006-01-02 15:04:05"))
+}