Number of stages of the baking process.
When ticking the ScriptableBakedReflectionSystem (see IScriptableBakedReflectionSystem.Tick, the current IScriptableBakedReflectionSystem is expected to bake data through stages.
Your own reflection system implementation may have a different number of stages, you should set the number here.
The BuiltinScriptableBakedReflectionSystem goes through 2 stages: BakeReflectionProbes, RenderRealtimeProbes.