affinity: add stale region cache to avoid cascading merges (#10103)#10106

ti-chi-bot[bot] merged 9 commits intotikv:release-8.5tikv/pd:release-8.5from

ti-chi-bot:cherry-pick-10103-to-release-8.5ti-chi-bot/pd:cherry-pick-10103-to-release-8.5Copy head branch name to clipboard