Don't extend the key ring cache lifetime beyond the default key lifetime

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Describe the bug

`CacheableKeyRing.WithTemporaryExtendedLifetime` should not extend the cache lifetime beyond the lifetime of the key ring's default key in order to avoid protecting data with an expired key. It only extends by two minutes but, AFAICT, it can be extended repeatedly, if each new attempt fails.

### Expected Behavior

Unfortunately, `CacheableKeyRing` doesn't expose a way to get to the default `IKey` - only the `IAuthenticatedEncryptor`, which doesn't have an expiration date. It would be straightforward to expose it on `IKeyRing`, but that type is public for historical reasons.

### Steps To Reproduce

I think you'd have to start the app in a state where the only available key was about to expire and then have generation of a new key fail (e.g. because of lack of access to AKV). But this is just theoretical and it's possible it can't arise in practice.

### Exceptions (if any)

_No response_

### .NET Version

_No response_

### Anything else?

_No response_