feat(`forge lint`): new lint rule: "unused imports"

[0xrusowsky]

Component

Forge

Describe the feature you would like

the linter should flag unused imports.

apparently it was removed from slither due to instability, but exists in solhint.

Additional context

No response

[Abhishekkochar]

🙋🏽‍♂️

[0xrusowsky]

@Abhishekkochar i'm almost done with this feature (forgot to assign the issue to myself)

tomorrow i start my holidays though and i'll be afk, so later today i'll push all my changes in a draft PR.
feel free to take over and bring it to the finish line!