Shutdown Kronos clock only after executors

[0xnm]

What does this PR do?

It is possible that Kronos is accessed from tasks still running on executors (like from telemetry caught during some I/O operation) and it will lead to the IllegalStateException, like here:

11-04 04:04:42.160: E/AndroidRuntime(7085): Process: com.datadog.android.sdk.integration, PID: 7085
11-04 04:04:42.160: E/AndroidRuntime(7085): java.lang.IllegalStateException: Service already shutdown
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.lyft.kronos.internal.ntp.SntpServiceImpl.ensureServiceIsRunning(SntpService.kt:142)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.lyft.kronos.internal.ntp.SntpServiceImpl.currentTime(SntpService.kt:98)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.lyft.kronos.internal.KronosClockImpl.getCurrentTime(KronosClockImpl.kt:19)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.lyft.kronos.KronosClock$DefaultImpls.getCurrentTimeMs(Clock.kt:39)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.lyft.kronos.internal.KronosClockImpl.getCurrentTimeMs(KronosClockImpl.kt:8)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.core.internal.time.KronosTimeProvider.getServerOffsetMillis(KronosTimeProvider.kt:25)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.telemetry.internal.TelemetryEventHandler.handleEvent(TelemetryEventHandler.kt:40)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.rum.internal.monitor.DatadogRumMonitor.handleEvent$dd_sdk_android_debug(DatadogRumMonitor.kt:385)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.rum.internal.monitor.DatadogRumMonitor.sendErrorTelemetryEvent(DatadogRumMonitor.kt:346)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.telemetry.internal.Telemetry.error(Telemetry.kt:21)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.log.internal.logger.TelemetryLogHandler.handleLog(TelemetryLogHandler.kt:22)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.log.internal.logger.InternalLogHandler.handleLog(InternalLogHandler.kt:40)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.log.Logger.internalLog$dd_sdk_android_debug(Logger.kt:566)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.log.Logger.internalLog$dd_sdk_android_debug$default(Logger.kt:556)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.log.Logger.log(Logger.kt:169)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.log.internal.utils.LogUtilsKt.errorWithTelemetry(LogUtils.kt:45)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.log.internal.utils.LogUtilsKt.errorWithTelemetry$default(LogUtils.kt:40)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.core.internal.persistence.file.batch.PlainBatchFileReaderWriter.writeData(PlainBatchFileReaderWriter.kt:50)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.v2.core.internal.storage.FileEventBatchWriter.write(FileEventBatchWriter.kt:48)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.rum.internal.domain.RumDataWriter.write(RumDataWriter.kt:43)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.rum.internal.domain.scope.RumViewScope$sendViewUpdate$1.invoke(RumViewScope.kt:726)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.rum.internal.domain.scope.RumViewScope$sendViewUpdate$1.invoke(RumViewScope.kt:660)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.core.internal.SdkFeature$withWriteContext$1.invoke(SdkFeature.kt:135)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.core.internal.SdkFeature$withWriteContext$1.invoke(SdkFeature.kt:134)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.v2.core.internal.storage.ConsentAwareStorage.writeCurrentBatch$lambda-0(ConsentAwareStorage.kt:74)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.v2.core.internal.storage.ConsentAwareStorage.$r8$lambda$VSlkAQX2O5ir-BQmjPcJjBdEv4c(Unknown Source:0)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at com.datadog.android.v2.core.internal.storage.ConsentAwareStorage$$ExternalSyntheticLambda0.run(Unknown Source:6)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
11-04 04:04:42.160: E/AndroidRuntime(7085): 	at java.lang.Thread.run(Thread.java:764)

This change modifies SDK shutdown sequence, so that Kronos is shutdown only after all executors are shut down, meaning there is no tasks running left.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)

[codecov-commenter]

Codecov Report

Merging #1127 (1aa8b50) into develop (a669a1f) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #1127      +/-   ##
===========================================
- Coverage    83.30%   83.25%   -0.05%     
===========================================
  Files          273      273              
  Lines         9372     9372              
  Branches      1504     1504              
===========================================
- Hits          7807     7802       -5     
+ Misses        1149     1148       -1     
- Partials       416      422       +6     

Impacted Files	Coverage Δ
...n/com/datadog/android/core/internal/CoreFeature.kt	91.60% <100.00%> (ø)
...android/rum/internal/ndk/DatadogNdkCrashHandler.kt	84.86% <0.00%> (-4.32%)	⬇️
.../android/rum/internal/monitor/DatadogRumMonitor.kt	92.05% <0.00%> (-0.57%)	⬇️
...ndroid/core/internal/persistence/file/EventMeta.kt	80.00% <0.00%> (ø)
...ain/java/com/datadog/opentracing/PendingTrace.java	58.62% <0.00%> (+0.86%)	⬆️
...nternal/persistence/file/batch/BatchFileHandler.kt	81.13% <0.00%> (+2.83%)	⬆️