Make blocksize configurable

[Gregory-Pereira]

This was particularly relevant when @oglok was testing the prefixAware caching demo. It would be nice to be able to configure block size but have it able to fallback to 256 as default.

Coderef: https://github.com/llm-d/llm-d-inference-scheduler/blob/main/pkg/scheduling/plugins/scorer/prefix_store.go#L19

[oglok]

I'll work on it.

[elevran]

@oglok - was this fully addressed by #120 ?
If so, please close