Extract inner Default classes to standalone top-level classes

[velo]

Summary

• Extracts 9 inner Default implementation classes from their parent interfaces into standalone top-level classes (DefaultClient, DefaultAsyncClient, DefaultContract, DefaultRetryer, DefaultEncoder, DefaultDecoder, DefaultErrorDecoder, DefaultInvocationHandlerFactory, DefaultQueryMapEncoder)
• Deprecates the original inner Default classes, reducing them to thin subclasses that delegate to the new standalone classes
• Updates all references (~54 files across 16+ modules) to use the new standalone classes

Test plan

• mvn test passes across all modules
• Deprecated inner classes still compile and work as thin wrappers for backward compatibility
• Client.Proxied correctly extends DefaultClient instead of the deprecated Client.Default

🤖 Generated with Claude Code