[server] add a looping task to free unused cnxsets capture by dead pyro When a pyro client disconnects, we're not necessarily notified so they can hang on to their session/cnxset forever. Don't let them do that. The hacky looping task is only installed when pyro is enabled. This optional activation save this very hacky patch from being rejected. closes #2825380

change_attribute_type('CWCache', 'timestamp', 'TZDatetime')
change_attribute_type('CWUser', 'last_login_time', 'TZDatetime')
change_attribute_type('CWSource', 'latest_retrieval', 'TZDatetime')
drop_attribute('CWSource', 'synchronizing')
add_attribute('CWSource', 'in_synchronization')