Fix a few mismatched method calls

Both `kria.pb.object.get` and `kria.pb.content` had method name typos in various setters, which would have resulted in an `IllegalArgumentException` when called. This pull request corrects all such issues, and a bit more (a missing argument in `kria.pb.content/Content->pb`'s `:charset` handler.

Found via `lein eastwood`, verified by hand.