LiteLLM normalizes every provider's cache fields onto
usage.prompt_tokens_details (cached_tokens + cache_creation_tokens).
The earlier fallback to usage.cache_read_input_tokens /
usage.cache_creation_input_tokens was wrong: Anthropic-shaped fields
only live there via a trailing setattr loop, and the canonical field
name on the wrapper is cache_creation_tokens (not _input_tokens).