Use Anthropic Cache Control for choose AI rule

It's a lot cheaper to use cache control, but the npm libs we use don't fully support it yet:

1. Caching tools isn't supported: https://github.com/vercel/ai/issues/3820
2. Cached token usage isn't returned: https://github.com/vercel/ai/issues/4335
3. Bedrock SDK doesn't yet support it: https://github.com/anthropics/anthropic-sdk-typescript/issues/507

We'd probably need to implement it manually if we want this to work right now: https://docs.anthropic.com/en/docs/build-with-claude/prompt-caching

Or make PRs to the above libraries.

We'd only use it on one ai call (Choose rule), although we use it use a lot, so it can lead to large cost savings.

Here's the WIP PR: https://github.com/elie222/inbox-zero/tree/anthropic-cache-control