AggregateClasspathDuplicateTest

Aggregate-classpath duplicate check for the deprecated :library facade.

The historical co.anitrend:retrofit-graphql artifact must expose exactly one copy of every legacy class: the legacy implementation lives in :compat (re-exported via api()), while :api, :runtime, :serialization-gson, and :serialization-kotlinx ship only their neutral contracts and the new transport codecs. Any second copy on this classpath means a legacy class was left behind in one of those modules.