[ty_test] Simplify column calculation using line_column
Instead of manually calculating character offsets, use line_column()
which does all the work for us:
1. Find the byte offset of the arrow in the comment text
2. Add that to the comment's TextRange to get the arrow's absolute position
3. Call line_column() on that position to get the character column
This is much simpler and lets line_column handle all the UTF-8/UTF-32
conversion complexity.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
