When the dedupe map rotates, the previous logic entirely cleared the map, meaning the message that triggered the rotation was immediately forgotten and could be duplicated immediately.
This change seeds the new map with the current message to prevent that. Also adds a defensive nil check.
Match rotation semantics to prior behavior by fully resetting the dedupe map
once the size limit is exceeded, and add focused tests for duplicate detection
and boundary rotation behavior.
Centralize dedupe map access behind a mutex-safe helper and use it in both
WeCom bot and WeCom app channels to eliminate concurrent map access races while
preserving current dedupe behavior.