Precompiled 2025-01-21-4121cc0

move PauseClient into Runtime (#33309)

PauseClient is really a global at the same level as Runtime -- based on the Runtime we might decide to advance time really quickly for tests, make randomness deterministic, start threads deterministically, or pause at specific labels to allow race conditions to be tested.

I was motivated to do this because I was adding new race tests for QueryCache, and I found myself passing PauseClient through many layers of code that already have Runtime and also already have multiple PauseClients. This felt redundant, and I can clean up a lot of code by just passing through the runtime.

One side effect is passing Runtime to a couple structs that don't already have it, like DatabaseSnapshot.

GitOrigin-RevId: f99a8625946fc2356103b5b8e294aa31fc6e0007