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 <noreply@anthropic.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

Author: stefano-garzarella