feat: implement MD007 ul-indent rule with perfect parity (#59)

[ekropotin]

Implements MD007 (ul-indent) rule for unordered list indentation consistency. This rule ensures list items are indented by the configured number of spaces with support for complex nesting scenarios and mixed list types.

Features

• Three configuration parameters:

  • indent: Spaces per nesting level (default: 2)
  • start_indent: Spaces for first level when start_indented=true (default: 2)
  • start_indented: Whether to indent first level (default: false)

• Smart list detection: Only checks unordered lists, ignores ordered lists

• Proper nesting handling: Correctly calculates indentation based on tree structure

• Mixed list support: Ignores unordered lists nested within ordered lists

Implementation

• Uses Token-based rule type for optimal performance with AST caching
• Comprehensive nesting level calculation with proper parent list validation
• Single-pass analysis with efficient tree traversal
• Perfect parity with original markdownlint validated through testing

Testing

• 14 comprehensive unit tests covering all configuration combinations
• 2 TOML configuration parsing tests
• 3 test sample files following project conventions
• Edge case coverage: empty documents, single items, nested structures
• Parity validation against original markdownlint

Documentation

• Complete rule documentation with examples and configuration details
• Updated README.md with rule status and configuration
• Comprehensive test samples demonstrating valid/invalid patterns

🤖 Generated with Claude Code