Nested generics support for Structs

[Praveen2112]

For a class Bean<T>(as Thrift struct) when we try to serialize/de-serialize for Bean<String> drift codec generates the code for the type String and maintains it the generated DriftCodec in a cache. But now if we try to do the same operation for Bean<Long> it tries to use the code generated for Bean<String>. This patch makes sure that we generate a separate DriftCodec for different type of T in Bean<T>.

[electrum]

I'm curious, how did you run into this issue? I didn't realize we supported this feature, and it seems like it would be hard to use in RPC which requires concrete types.

[Praveen2112]

@electrum Thanks for the review. Resolved the above issues. We currently use drift-codec for only for serialization/de-serialization (as a replacement for JSON serialization/de-serialization). Like List<T> we have a custom object Bean<T> which has to be serialized/de-serialized. First we created a ThriftCodec for Bean<String> and it was working fine , when we try to create a ThriftCodec for Bean<Long> and try to serialize a instance of Bean<Long> we faced this issue.

[Praveen2112]

@electrum Any other changes that I need to do ? Ideally it might resolve the issue discussed here (#70 (comment)) ?