Linux tool to monitor bandwidth consumption of a specific process (PID)

So since I didn't find any easy/clear/"hit the ground running" solution, I had to made a modest one, fixes, refactoring and more options to come.

-> https://github.com/AymenDaoudi/NeTraf

Have you looked at the tool atop? According to the man page for it:

"Network load is shown per process if the kernel module `netatop' has been installed."