| 1234567891011121314151617181920 | from typing import Optionalfrom pydantic import BaseModelclass PreviewDetail(BaseModel):    content: str    child_chunks: Optional[list[str]] = Noneclass QAPreviewDetail(BaseModel):    question: str    answer: strclass IndexingEstimate(BaseModel):    total_segments: int    preview: list[PreviewDetail]    qa_preview: Optional[list[QAPreviewDetail]] = None
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