fix(md): Remove <!-- end list --> from terminal output

[JeanMertz]

comrak's CommonMark serializer emits <!-- end list --> between adjacent lists and before indented code blocks as a round-trip hint — it helps the serializer's own output be re-parsed without ambiguity. The terminal renderer has no such obligation; its output is never fed back into a markdown parser, so the marker is pure visual noise.

Removed the block that conditionally wrote the marker and changed format_list from returning fmt::Result to returning (), since it no longer performs any fallible writes.