interface: speed up handle_disconnect via shorter flush-buffer-timeout
interface: speed up handle_disconnect via shorter flush-buffer-timeout

Note in particular that _RSClient.__aexit__ calls session.close()
so a lot of time can pass between interface.taskgroup raising and
handle_disconnect seeing the exception.

related https://github.com/spesmilo/electrum/issues/7677

spesmilo/electrum,spesmilo/electrum,pooler/electrum-ltc,pooler/electrum-ltc,pooler/electrum-ltc,spesmilo/electrum,wakiyamap/electrum-mona,wakiyamap/electrum-mona,spesmilo/electrum,wakiyamap/electrum-mona,pooler/electrum-ltc,wakiyamap/electrum-mona