add knip

[juliusmarminge]

agents love leaving old stuff behind. knip (https://knip.dev/) is a good tool to mitigate this by enforcing no code is unused.

we should set it up with the proper config for our monorepo

[lahiruramesh]

I would like to address this issue.

[Dhirenderchoudhary]

@juliusmarminge I have knip in one of my contributing can. i go ahead with this issue if you assign me.

[juliusmarminge]

Resolved by #9962 (Knip stack #9958–#9962).