使用dynamic修饰后，didSet仍然不执行

使用的HandyJson版本是5.0.2，变量使用dynamic修饰后，didSet仍然不执行。
```
dynamic var state:Int = 0 {
didSet {
switch state {
case 1:
typeTuple = ("开始",0xFF8833)
case 2:
typeTuple = ("处理",0xFF8833)
default:
typeTuple = ("",0xFF8833)
}
}

willSet {

}
}
```

Reproduce the reported behavior with HandyJSON 5.0.2 using the provided dynamic state property and its didSet observer. Then inspect the serialization and property-mapping entry points to determine whether deserialization triggers the observer; done means the behavior is corrected or its limitation is clearly documented with a regression test.

Written by the indexing model from the issue text.