- testhelpers_db: retry truncateAllTables up to 3 times on deadlock,
which occurs when previous tests' goroutines still hold DB connections
- handlers_rengoku_integration_test: restore rengoku_score table after
TestRengokuData_SaveOnDBError drops it, preventing cascading failures
in all subsequent rengoku tests
- client_connection_simulation_test: fix TestClientConnection_PacketDuringLogout
to accept both race outcomes (save-wins or logout-wins) since both
handlers independently load from DB and last-writer-wins is valid