* Report cached prompt tokens
Add prompt_eval_cached_count to native responses and expose equivalent cached-token fields through the OpenAI- and Anthropic-compatible APIs. Keep prompt_eval_count as the logical input total while excluding cache hits from CLI and benchmark prefill rates. Surface processed and cached prompt counts in benchmark output.
Collect cache counts from llama-server and MLX, preserve coherent metrics across two-pass structured generation.
Fixes#8008
Related to #15758
* review comments