Protobuf deserialization is slow and the bottleneck for a vectormap application

The MapBox vector map standard uses Protobuf to decode the coordinates of streets, houses, etc. (https://docs.mapbox.com/api/maps/vector-tiles/).

In an attempt to implement this standard on basis of QtGrpc (https://github.com/cecilianor/Qt-thesis/tree/main) , we found that the deserialization is very inefficient. A tile with a size of 200 KB takes about 2 seconds to deserialize on a new laptop. Usually around 4-16 tiles need to be loaded to show a map. Competitors do this basically instantly.

This example is a good opportunity to profile real world usage and to eliminate the bottleneck in the protobuf deserialization.