FORMAT with ~A/~S/~D/~F/~%/~&/~T/~P/~{...~}/~^; cl-fmt-loop,
cl-fmt-find-close, cl-fmt-iterate, cl-fmt-a/cl-fmt-s helpers.
Fix substr(start,length) semantics throughout: SUBSEQ end formula
corrected to (- end start), cl-fmt-loop char extraction fixed.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>