Implement/improve automated package claim checks and notifications

Following last month's meeting https://meetbot.debian.net/debian-lts/2025/debian-lts.2025-03-27-14.00.html

write an issue (in lts-extra-tasks) for implementing an automated package claim age check + associated notifications

Currently we have an automated package claim age check that looks at data/xla-needed.txt NOTEs and unclaim the package if the last NOTE is > 2 weeks old.

Multiple improvement ideas were suggested, including:

• Send personal, advance notifications about package claims expiration
• Ensure re-claimers do add a new NOTE with the updated package status
• Block self re-claims for a few days if no progress was made, to entice other contributors to step in
• Infer package activity from associated Git repo (note: doesn't necessarily free one from adding regular NOTEs)
• (discussion log is not very clear really, please re-read :))

cc @roberto