Fix column annotation alignment for CJK and fullwidth characters

[SergeyGildenshtern]

Summary

This PR fixes incorrect column alignment in generated annotations when column names or comments contain fullwidth or CJK characters.

Previously, the width calculation relied on:

elem.bytesize == 3

This approach is incorrect because UTF-8 byte size does not correspond to terminal display width. As a result, annotations could become misaligned when using certain Unicode characters.

This PR replaces the byte-size heuristic with a simplified Unicode range-based implementation that accounts for characters typically rendered as double-width in monospace terminals (CJK and fullwidth forms).

Problem

When using certain Unicode characters in column comments (e.g. currency symbols), annotation formatting could shift and break alignment.

Example case:

# frozen_string_literal: true

class TestMigration < ActiveRecord::Migration[8.0]
  def up
    create_table :payments do |t|
      t.decimal :value, null: false, comment: 'The amount(€) of payment'
      t.datetime :created_at, null: false
    end
  end
end

Before this change, alignment could be inconsistent depending on the characters used.

Before (broken alignment)

After (correct alignment)

Limitations

This remains a simplified wcwidth implementation and does not support:

• Emoji
• Grapheme clusters (e.g. family emoji sequences)
• Combining marks
• Zero-width joiners
• East Asian ambiguous-width characters

If full Unicode terminal-width compliance is ever required, the implementation could be replaced with a dedicated library such as unicode-display_width.

[drwl]

Thanks for adding this + the write up. As a person that uses mostly ascii characters, having other people help with unicode is greatly appreciated 👍