When NixOS is already running and Tor is restarted due to config
changes, `/var/lib/tor/state` may be present even when Tor has not
yet finished setting up onion services.
This caused the previous version of `onion-addresses` to not wait for
Tor and to skip not yet present onion service files.
`onion-addresses` now waits until each required onion service file
has appeared.
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