WecomCallbackAdapter declared a _seen_messages dict and
MESSAGE_DEDUP_TTL_SECONDS constant but never actually checked
them in _handle_callback(). WeCom retries callback deliveries
on timeout, and each retry with the same MsgId was treated as
a fresh message and queued for processing.
Fix: check _seen_messages before enqueuing. Uses the same TTL-
based pattern as MessageDeduplicator (fixed in #10306) — check
age before returning duplicate, prune on overflow.
Closes#10305
44941f0ed1