Schedule external stats sync on battery level change with a delay

and fix locking in scheduleCpuStatsSyncDueToWakelockChange().

Bug: 74146897
Test: atest cts/hostsidetests/incident/src/com/android/server/cts/BatteryStatsValidationTest.java
Test: atest core/tests/coretests/src/com/android/internal/os/BatteryStatsTests.java
Change-Id: I2891dfb8a0aedf429232f45e26deab93c738506e