Generate nested result types as inner records in graphql-apt

[velo]

Summary

• Nested result types (e.g., Location from location { planet sector }) are now generated as public record inner classes within their parent result type, instead of separate top-level files
• Each query result type gets its own scoped nested type definitions, preventing conflicts when different queries select different fields from the same GraphQL type
• Added conflict detection: if two queries use the same return type name but select different fields, a compilation error is reported
• Replaced test schema with Star Wars-themed types (from graphql.org) for better readability

Test plan

• All 20 tests pass (mvn clean test -pl graphql-apt)
• New test: conflictingReturnTypesReportsError — same return type, different field selections → error
• New test: sameReturnTypeSameFieldsSucceeds — same return type, same selections → OK
• New test: innerClassContentIsCorrect — verifies exact structure of generated inner records
• New test: differentQueriesDifferentNestedFields — two queries selecting different Location fields each get their own inner class

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