The FromProto and IntoProto macros provide an easy way to convert Rust struct to
corresponding Protobuf struct, or vice versa. For example:
#[derive(FromProto, IntoProto)]
#[ProtoType(ProtobufStruct)]
struct RustStruct {
field1: Field1,
field2: Field2,
...
fieldn: FieldN,
}
It requires that all fields (Field1, Field2, ..., FieldN) implement FromProto trait if
we want to derive FromProto for RustStruct. Same for IntoProto trait.