GSOC2025: Json Library for D, weekly update #9

[Gaofei]

Add caseInsensitive as a compile-time parameter to the 
DefaultDeserializationPolicy. We can simply enable it by:
```d
auto policy = DefaultDeserializationPolicy!true();
```
https://github.com/schveiguy/jsoniopipe/pull/57

Try to implement maxDepth check and policy-enabled JSONValue 
deserialization.
https://github.com/schveiguy/jsoniopipe/pull/58