Fix DataRepository to return trait implementation instead of lambda

[Copilot]

The DataRepository.apply method was returning a lambda function instead of a proper trait instance, breaking the type contract.

Changes

• Replaced lambda (query, batchSize) => { ... } with anonymous class implementing DataRepository[F]
• Added explicit override def streamData method declaration

Before/After

// Before: returns lambda, not DataRepository[F]
def apply[F[_]: Async](xa: Transactor[F]): DataRepository[F] =
  (query: String, batchSize: Int) => { ... }

// After: returns proper trait instance
def apply[F[_]: Async](xa: Transactor[F]): DataRepository[F] =
  new DataRepository[F] {
    override def streamData(query: String, batchSize: Int): Stream[F, SampleData] = { ... }
  }

This pattern matches the implementation in S3Writer.apply.

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