Add prompt_execution_ids and workflow_execution_ids to WorkflowExecutionFulfilledBody

[devin-ai-integration]

Adds two new optional fields to WorkflowExecutionFulfilledBody to match the backend schema changes in https://github.com/vellum-ai/vellum/pull/19204. These fields hold direct child prompt execution IDs and subworkflow execution IDs for cost calculation purposes.

Review & Testing Checklist for Human

• Verify the field types (Optional[list[UUID]]) match the backend schema (string[] | null with UUID format)
• Consider if additional test coverage is needed for non-None values of these fields
• Verify UUID list serialization works correctly without a custom serializer

Notes

• Requested by: @marlenc3
• Session: https://app.devin.ai/sessions/de7d61b6c91948c09a31463899c1087e

[devin-ai-integration]

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