Module parser/rules/block

Central registry for all block-level parser rules.

This module imports every block rule, re-exports each one individually (for selective use), and assembles them into the ordered blockRules array that the main parser iterates through.

Rule ordering matters: rules earlier in the array are tried first. Line-start-only rules (comments, headings, lists, etc.) are naturally filtered by the requiresLineStart flag, but among rules that share a start token (e.g. BLOCK_OPEN), position in this array determines priority. For example, codeBlockRule is tried before collapsibleRule because both start with BLOCK_OPEN but code blocks should be matched first.

The paragraph rule is deliberately excluded from the array -- it serves as a fallback and is exported separately as blockFallbackRule.