Add tool to detect inactive GitHub codeowners

Introduces a Python script that checks CODEOWNERS against GitHub activity
(reviews, PR/issue comments) over a configurable time period.

The script was initially included in
rust-vmm/community#188

Co-Authored-By: Claude <[email protected]>
Signed-off-by: Stefano Garzarella <[email protected]>

Author: stefano-garzarella