minor refactoring of precise-prefix-cache scorer plugin

[vMaroon]

Summary

• Removed redundant logging: a lot of the logging was either duplicated, or adds no valuable info
• Refactored a redundantly repeated call: the preprocessor initialization performs a C call that checks a per-process initialization. Practically, after the first call, this is wastefully going into C to print that it's already initialized and return 0. See it here: https://github.com/llm-d/llm-d-kv-cache-manager/blob/038a91c28d24a40389f28432f6cfac4cd358d1fb/pkg/preprocessing/chat_completions/cgo_functions.c#L40

This manner of initializing/use of the preprocessor was previously tested, but we'll re-benchmark an image built from this code. Once ready will attach here.

[nirrozenbaum]

/lgtm
/approve