Function build_chunk 

fn build_chunk(
    file_id: Uuid,
    file_path: &Path,
    chunk_index: u32,
    output: ChunkOutput,
    embedding: Vec<f32>,
    content_type: &ContentType,
    mime_type: &str,
    model_name: &str,
    now: DateTime<Utc>,
) -> Chunk

Build a Chunk from chunk output and embedding.