Variable listRuleConst

Block rule for marker-based lists (* bullet, # numbered).

Parsing strategy:

1. Verify the first token is LIST_BULLET or LIST_NUMBER at line start.
2. Collect consecutive list lines, recording each item's depth (number of leading spaces), type (bullet/numbered), and inline content.
3. Feed the flat depth array into processDepths() with type comparison, producing a nested tree.
4. Convert the tree into list AST elements via buildListElement().