[ty_test] Fix hover column calculation to use line position
The previous implementation calculated the down arrow position within
the comment text, but then incorrectly used that as an offset into the
target line. This only worked if the comment started at column 0.
Now we properly calculate the column position by:
1. Finding the arrow offset within the comment text
2. Getting the comment's column position in its line
3. Adding these together to get the arrow's column in the line
4. Using that column to index into the target line
This fixes hover assertions when comments are indented or don't start
at the beginning of the line.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
