[spm] Improve service performance by caching object UIDs.

The `spm` implementation currently caches object labels and performs UID lookup operations during certain API calls. Caching object UIDs per SKU can help improve performance significantly as the lookup operation may not be optimized for performance.

Start by locating the spm implementation and the existing object-label caching and UID lookup paths. Identify which API calls perform lookups and how SKUs are represented; the work is done when object UIDs are cached per SKU, repeated lookups are avoided, and existing behavior remains correct.

Written by the indexing model from the issue text.