features/unmarshal_unique: Maps with string-keys

[coxley]

Summary

Hey folks! I've been wanting to start using #140 and while we have some good candidates for it, one of the biggest benefits on my side would be to intern string keys inside some maps.

Any idea how tough it would be to extend to that use-case? Any gotchas come to mind?

I'm not opposed to implementing it if not — but don't care either way. :)

Example Proto

message Foo {
  string identifier = 1;
  // A bunch of tags for some entity, where there are loads of common keys across
  // 100k of messages being processed at the same time
  map<string, AttributeValue> attributes = 2;
}