o Minor features (fallback directory mirrors): - Give each fallback the same weight for client selection; restrict fallbacks to one per operator; report fallback directory detail changes when rebuilding list; add new fallback directory mirrors to the whitelist; update fallback directories based on the latest OnionOO data; and any other minor simplifications and fixes. Closes tasks 17158, 17905, 18749, bug 18689, and fixes part of bug 18812 on 0.2.8.1-alpha; patch by "teor".