Function sheet_to_raw_buffer 

pub fn sheet_to_raw_buffer(
    ws: &WorksheetXml,
    sst: &SharedStringTable,
) -> Result<Vec<u8>>

Serialize a worksheet’s cell data into a compact binary buffer.

Reads cell data directly from WorksheetXml sheet data, resolving shared string references via sst. The resulting buffer uses either dense or sparse layout depending on cell density relative to the bounding rectangle.