v3.15.63

Commits since CHANGELOG generation

946cc8b chore(release): bump version to 3.15.63 (#23793)
e68edca fix: extract timeout mock helper (#23792)
c109332 plan: add t3591 person-stats timeout follow-up (#23763)
617d596 chore: update simplification state registry
90f97cd fix: harden supply-chain test cleanup guard (#23790)