[Proposal] switch to streaming mode in ExcelJs

[Siemienik]

Streamming

Exceljs has streamming api, this should works perfectly for us

https://github.com/exceljs/exceljs#streaming-xlsx-readercontents

[Siemienik]

As described in The Index of Proposals (#144), it will be reopened if accepted.

🗣️ 🗣️ 🗣️ 🗣️ Any discussion here is wanted.