GetDataUsageTool
Returns mobile (cellular) data usage over a look-back window. Prefers android.app.usage.NetworkStatsManager.querySummaryForDevice which requires the PACKAGE_USAGE_STATS special-access grant; on SecurityException/failure — or on API < 29, where a null subscriber id yields an empty (all-zero) summary — it falls back to android.net.TrafficStats cumulative-since-boot totals (which ignore the days window and add a note). Param days (1-90, default 30). Output: bytes_rx, bytes_tx, plus query_period_days on the windowed path or note (and no query_period_days) on the since-boot fallback path. Returns ToolResult.error only when even TrafficStats is unsupported.