[python API] add package download event

Hello,

Currently we have:
PT_DOWNLOAD - start download
PT_DOWNLOAD_PKGS - list of packages to download.
The void until:
PT_GPGCHECKPT_GPGCHECK

This void takes a lot of time as packages are downloaded.

May I suggest adding an event before/after each package is downloaded?

Maybe I missed this exiting functionality, but all I see is raw text logs that may provide this information if I parse the data.

Regards,
Alon Bar-Lev.