Zstd for compressing package index databases

Currently, the size of extra.db.tar.gz is about 7.7 MiB. If zstd is used instead of gzip, the compressed [extra] database will be about 7% (level 3, default) or 13% (level 12) smaller.

This proposed change would benefit people with slow connections. The benefit would be small (1~2 seconds for 500 KiB/s) and infrequent, but it's a second where people would likely be paying some attention to the screen, so it might arguably improve the experience for some.

In your opinion, is this worth considering, or is it an over-optimisation?

(Originally posted at https://bbs.archlinux.org/viewtopic.php?id=303693. Allan pointed out in reply that larger savings can be achieved by removing the %PGPSIG% field in the db.)