ProcessorSlot should be stateless

## Issue Description
Now sentinel will create a new list for every resource because some of the slots are bound to specific resource.

### Describe what happened (or what feature you want)
Many slots will be created in memory.

### Describe what you expected to happen
They should be reusable.

### Anything else we need to know?
Related slots are `ClusterBuilderSlot` and `NodeSelectorSlot`.

Start by reading the ProcessorSlot implementation and tracing how slots are created and bound to resources. Compare it with ClusterBuilderSlot and NodeSelectorSlot to identify the state that prevents reuse. Done means these related slots can be reused without creating resource-specific lists, with existing slot behavior preserved.

Written by the indexing model from the issue text.