The QQ channel's _run_bot() used a fixed 5-second reconnect interval with
no backoff. When the network is unavailable (e.g., DNS failure), this
produces excessive botpy SDK error tracebacks every 5 seconds, flooding
logs.
botpy's Client.bot_connect() catches ws_connect() exceptions internally
and calls BotWebSocket.on_error(), which logs a full traceback and
immediately re-queues the session. The outer _run_bot() except never
fires for the reported DNS failure path.
Override bot_connect() on the _Bot subclass to:
- Apply exponential backoff (5s -> 300s cap) before re-queuing the session
- Log network errors (ClientConnectorDNSError, ClientConnectorError,
OSError) compactly without traceback
- Reset backoff on successful connection
- Still call traceback.print_exc() for non-network errors
The outer _run_bot() loop retains exponential backoff as a fallback for
exceptions that escape start() entirely. The botpy library logging
redirect is elevated to ERROR to suppress redundant connection tracebacks.
Consistent with patterns already used in matrix.py and napcat.py.
Add 7 regression tests covering:
- DNS error applies backoff and re-queues session
- No traceback printed for network errors
- ClientConnectorError also triggers backoff
- Backoff doubles and caps at 300s
- Successful connection resets backoff
- Non-network errors still re-queue without backoff
- _is_network_error() classification
Fixes#4767
