feat(cryptox): 自 go-hua/common 迁入 MD5 摘要工具并独立成包

- 字符串/字节集/文件 MD5，附单元测试、examples/cryptox 例程与包 README

cryptox/cryptox_test.go

@@ -0,0 +1,33 @@
+package cryptox
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestMd5(t *testing.T) {
+	want := "5d41402abc4b2a76b9719d911017c592"
+	got, err := GetMd5ByStr("hello")
+	if err != nil || got != want {
+		t.Errorf("GetMd5ByStr = %q, %v, want %q", got, err, want)
+	}
+	got, err = GetMd5ByBytes([]byte("hello"))
+	if err != nil || got != want {
+		t.Errorf("GetMd5ByBytes = %q, %v", got, err)
+	}
+}
+
+func TestGetFileMd5(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "test.txt")
+	if err := os.WriteFile(path, []byte("hello"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	got, err := GetFileMd5(path)
+	if err != nil {
+		t.Fatalf("GetFileMd5: %v", err)
+	}
+	if got != "5d41402abc4b2a76b9719d911017c592" {
+		t.Errorf("GetFileMd5 = %q", got)
+	}
+}