add Client::Base#save_started_at, #save_finished_at, #elapsed_save_time. before_save :touch_save_started_at, after_save :touch_save_finished_at
refactor save_time to request_time. Add specs to #destroy for request_started_at, finished_at, elapsed_request_time
add #elapsed_request_time_ms
Release 2.3.2. Add request timer