OverflowException in MetricsEventManager.RaiseMetricsPerFunctionEvent

Kusto logs are showing an overflow exception here for some customer apps:

```
System.OverflowException : Value was either too large or too small for a UInt64.
at System.Decimal.ToUInt64(Decimal d)
at System.Convert.ToUInt64(Decimal value)
at Microsoft.Azure.WebJobs.Script.WebHost.Diagnostics.MetricsEventManager.FunctionActivityTracker.<>c.b__29_1(IGrouping`2 functionGroups)
at /_/src/WebJobs.Script.WebHost/Diagnostics/MetricsEventManager.cs : 556
at System.Linq.Enumerable.SelectEnumerableIterator`2.MoveNext()
at Microsoft.Azure.WebJobs.Script.WebHost.Diagnostics.MetricsEventManager.FunctionActivityTracker.RaiseMetricsPerFunctionEvent()
at /_/src/WebJobs.Script.WebHost/Diagnostics/MetricsEventManager.cs : 565
at Microsoft.Azure.WebJobs.Script.WebHost.Diagnostics.MetricsEventManager.FunctionActivityTracker.TimerFlush(Object state)
at /_/src/WebJobs.Script.WebHost/Diagnostics/MetricsEventManager.cs : 382
```

Start in src/WebJobs.Script.WebHost/Diagnostics/MetricsEventManager.cs at the reported lines 556 and 565, tracing the UInt64 conversion inside RaiseMetricsPerFunctionEvent. Reproduce or isolate the metric values that trigger the overflow, then verify that metrics flushing completes without the exception for those values.

Written by the indexing model from the issue text.