'MessageType' support

I am in the process of implementing protovalidate in pure-python using cel-python have push things as far as I can from the outside leaving me the following 7 issues:


1-2, 5-7: cel-python doesn't support nano resolution
3: cel-python doesn't support protobuf messages
4: cel-python doesn't check the data is valid before applying the regex

I am mostly interested (3). I have implemented most of the logic needed to seamlessly integrate protobuf into cel-python, by materializing protobuf messages as a map; however, as protobuf supports cycles in the type system, this is insufficient (as well as inefficient). I am curious if there is any interest to add support, potentially based on the code I have already written.