Better type annotation syntax is needed. 

For example, `get_rpc_header(rpc, 'appnet-rpc-id', rpc_id)` needs to know the type of `rpc_id` to generate C++ type cast code. for now we just use:
```
rpc_id = 0
rpc_id = get_rpc_header(rpc, 'appnet-rpc-id', rpc_id)
```

which is not that pleasing to the eye.