* feat: add initial speculative benchmark logic
* feat: enhance speculative benchmark with position tracking and JSONL prompt support
* feat: enhance speculative benchmark with batch processing and parameter limiting
* Refactor spec-bench to support Markdown output and new prompt files
* spec-bench: finalize interface inputs and reports
* spec-bench: finish report cleanup
* spec-bench: remove unused code
* spec-bench: improve docs and output details for metrics clarity
* spec-bench: align checkpoint mode with current main
