Align/merge the the two prefix-cache aware routing plugins

[ahg-g]

We currently have two implementations for prefix-cache aware routing, one in this project and one in upstream IGW. Ideally the one we have in llm-d informs any improvements that should be done to the upstream if there any, and deprecate the one we have in this repo to avoid having maintain two.

[elevran]

@kfirtoledo - can you please provide an update on status, next steps, etc.?
If there's ongoing GIE work to align the two, please link relevant issue.

[kfirtoledo]

The GIE prefix scorer was updated to use the standard GoLang LRU Cache (PR 928).
The next step is to move part of the P/D logic out of the prefix scorer. Once this separation is complete, we can remove the redundant implementation and use only the GIE prefix scorer.