Cleanup cache proxy pattern

What does this MR do?

Make the cache proxy pattern easier to read, removing redundant casts.

Why was this MR needed?

This design looks like it originally intended to be more succinct, but over time, it hasn't aged well.

What's the best way to test this MR?

There should be no functional change here. Where there's a refactor (such as generateObjectName), we already have test coverage.

We also have an integration test that checks caches work.

What are the relevant issue numbers?

Closes #28850 (closed)