ORDERED_RE only captured item text and discarded the source number, and the
parse loop broke on the first blank line — so loose numbered lists (blank lines
between items) re-indexed every item to 1.
- capture the prefix number and emit it as MdBlock.Ordered.index
- treat a blank line as list-internal when the next non-blank line is another
ordered item, so loose lists stay one ordered list
- keep sequential numbering for tight lists (1,2,3) and honor custom starts
add regression tests in MarkdownTextFeatureTest (loose, custom-start, tight).
Co-authored-by: M57 <hy4ri@users.noreply.github.com>