Add blocklist candidate listing, scan trigger, status update,
push/unblock to Pi-hole, and connection test endpoints.
Add pihole_url/version/api_key and router_source_ids/device_names
fields to SettingsBody and prefs handling in patch_settings.
Add PiholeClient.__post_init__ validation so 503 fires naturally
when url/api_key are unconfigured (mock-safe: bypassed in tests).
PiholeClient dataclass supporting both Pi-hole v5 (PHP /admin/api.php)
and v6 (REST /api/) with public block/unblock/test_connection methods.
9 tests covering both API versions, auth flow, and error handling.
