[core] Optimize String format in CacheManager

[JingsongLi]

Purpose

Tests

[leaves12138]

Looks good to me.

This change is a small cleanup in CacheManager: it switches from eager String.format(...) to the existing Preconditions.checkNotNull(reference, template, args...) overload, so the error message is only formatted on the null path. The checkNotNull overload supports %s templates, so the behavior remains equivalent when the cache lookup unexpectedly returns null.

I reviewed the diff and checked the corresponding Preconditions API. The existing failing CI job looks unrelated to this one-line change.