Rare crash when launching multiple clients

## Background
We're using Cesium to build a multiplayer system in Unity. As part of our testing protocol, we have multiple clients that will boot up and connect to a shared server.

## Error
When our test script is executed, occasionally we will get the following stack trace:

```
0x00007FFD236353AC (KERNELBASE) RaiseException
0x00007FFCEB3D6BA7 (VCRUNTIME140) CxxThrowException
0x00007FFC9447B5E9 (CesiumForUnityNative-Runtime) DotNet_CesiumForUnity_CesiumPolygonRasterOverlay_CreateImplementation
0x00007FFC94479271 (CesiumForUnityNative-Runtime) DotNet_CesiumForUnity_CesiumPolygonRasterOverlay_CreateImplementation
0x00007FFC943EF8DD (CesiumForUnityNative-Runtime) DotNet_CesiumForUnity_CesiumPolygonRasterOverlay_CreateImplementation
0x00007FFC943EF5DD (CesiumForUnityNative-Runtime) DotNet_CesiumForUnity_CesiumPolygonRasterOverlay_CreateImplementation
0x00007FFC93A2B381 (CesiumForUnityNative-Runtime) DotNet_CesiumForUnity_CesiumPolygonRasterOverlay_CreateImplementation
0x00007FFC93A2BB15 (CesiumForUnityNative-Runtime) DotNet_CesiumForUnity_CesiumPolygonRasterOverlay_CreateImplementation
0x00007FFC939DB8CA (CesiumForUnityNative-Runtime) DotNet_CesiumForUnity_CesiumPolygonRasterOverlay_CreateImplementation
0x0000012EF928BE14 (Mono JIT Code) (wrapper managed-to-native) CesiumForUnity.Cesium3DTileset:DotNet_CesiumForUnity_Cesium3DTileset_Update (intptr,CesiumForUnity.Cesium3DTileset/ImplementationHandle)
0x0000012EF928BCC3 (Mono JIT Code) CesiumForUnity.Cesium3DTileset:Update ()
```

This crash only seems to affect one of the clients we spawn in our testing script. The testing script is below:

```
start "Test1" Client.exe -playerName 1 -serverIp 127.0.0.1 -hideDebugGUI true
start "Test2" Client.exe -playerName 2 -serverIp 127.0.0.1 -hideDebugGUI true
```

This crash seems to happen when ever we launch two or more clients within about 5 seconds of each other. If we wait longer than that, the crash does not seem to ever occur.

## Technical Details
Unity Version: 22.3.18f1
CesiumForUnity Version: 1.9.0
We could not replicate the crash in the CesiumForUnity sample project

## Conclusion
This is a rather annoying, but likely low priority, crash in our testing pipeline. It appears to be caused by something in the C++ implementation of the code, though my C++ skills are not sufficient to determine what. If there is a simple workaround we can implement, that would help us out a lot! The full stack trace and memory dump are available on request.

Start by running the supplied test script with Unity 22.3.18f1 and CesiumForUnity 1.9.0, launching two Client.exe instances within five seconds. Investigate the Cesium3DTileset.Update and CesiumPolygonRasterOverlay_CreateImplementation paths shown in the stack trace, requesting the full memory dump if needed. Done means the rapid multi-client launch no longer produces the reported crash.

Written by the indexing model from the issue text.