`StorageCredentialCache` can provide unusable credentials

### Describe the bug

The code design of `StorageCredentialCache` ensures that credentials are cached for some defined amount of time. Returned cached credentials are guaranteed to be valid when retrieved from the cache, but there's no guarantee that the returned credentials will be valid for the next N minutes. It can happen that the vended credentials returned to clients are not or not long enough valid.

### To Reproduce

_No response_

### Actual Behavior

_No response_

### Expected Behavior

_No response_

### Additional context

_No response_

### System information

_No response_

Start by locating StorageCredentialCache and tracing its credential retrieval callers and expiry checks. Confirm the required future-validity window with maintainers, then add a regression test showing that returned credentials remain usable for that window; done means the cache no longer vends credentials that expire too soon.

Written by the indexing model from the issue text.