StatsPerUidLogger: fixed StrictMode policy violation

- The caller of getBatteryUsageStats must call close() on the resulting BatteryUsageStats object

Flag: com.android.server.power.optimization.add_battery_usage_stats_slice_atom

Bug: 324602949
Test: adb shell cmd stats pull-source 10209; and review logcat for warnings
Change-Id: Ie4f81c7675b811c5b6b69fb33d5e926b05d0c02c