Add tablerow tag support

[sebastienros]

Summary

Implements the Liquid tablerow tag that generates HTML table rows for every item in an array.

Features

• Basic iteration: {% tablerow item in collection %}{% endtablerow %}
• cols: parameter for column count
• limit: parameter to limit iterations
• offset: parameter to start at an offset
• Full tablerowloop object with all properties:
  • index, index0 - 1-based and 0-based iteration index
  • col, col0 - 1-based and 0-based column index
  • row - 1-based row index
  • first, last - boolean for first/last iteration
  • col_first, col_last - boolean for first/last column in row
  • length - total number of iterations
  • rindex, rindex0 - reverse index

Implementation

The implementation follows the Shopify Liquid Ruby reference implementation and matches the same parser pattern as the existing for tag.

Files Changed

• Fluid/Ast/TableRowStatement.cs - AST node for tablerow tag
• Fluid/Values/TableRowLoopValue.cs - tablerowloop object
• Fluid/FluidParser.cs - Parser registration
• Fluid/Parser/TagParsers.cs - TableRowModifier struct
• Fluid/Ast/AstVisitor.cs - Visitor support
• Fluid/Ast/AstRewriter.cs - Rewriter support

Testing

All existing tests pass.