Fix top-level deferred patch registration

[Copilot]

Top-level @defer patches could be dropped when enableEarlyExecution was disabled and initial field execution completed synchronously. buildResponse observed no registered subsequent payloads and returned a non-incremental result before deferred patches were started.

• Execution ordering

  • Register top-level deferred patches before calling buildResponse for queries and mutations when early execution is disabled.
  • Reuse the existing patch execution helper to keep behavior aligned with early execution paths.

• Regression coverage

  • Add coverage for a synchronous top-level selection with an async deferred field:

{
  critical
  ... @defer {
    deferred
  }
}

This now produces an initial incremental response with hasNext: true, followed by the deferred payload.

[azure-pipelines]

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