When a WebSocket-based platform adapter (e.g. QQ Bot) temporarily
loses its connection, send() now polls is_connected for up to 15s
instead of immediately returning a non-retryable failure. If the
auto-reconnect completes within the window, the message is delivered
normally. On timeout, the SendResult is marked retryable=True so the
base class retry mechanism can attempt re-delivery.
Same treatment applied to _send_media().
Adds 4 async tests covering:
- Successful send after simulated reconnection
- Retryable failure on timeout
- Immediate success when already connected
- _send_media reconnection wait
Fixes#11163
504e7eb9e5