Add explicit test for Protobuf Ruby depth limit of 64
Add explicit test for Protobuf Ruby depth limit of 64

This gives a more realistic example of a nesting-related parsing failure
that hits at 64 messages deep (easier to reach with many JOINs) and adds
additional context from the Protobuf Ruby implementation details.

jcsjcs/pg_query,jcsjcs/pg_query,lfittl/pg_query,jcsjcs/pg_query,lfittl/pg_query