llama-bench : add --no-warmup flag (#14224) (#14270)
Add no_warmup parameter to cmd_params struct and command-line parsing to allow users to skip warmup runs before benchmarking.
- Add no_warmup boolean field to cmd_params struct
- Add --no-warmup command-line argument parsing
- Add help text documentation for the new flag
- Wrap existing warmup logic in conditional check
- Maintain full backward compatibility (warmup enabled by default)
Addresses #14224
