Add Russian and Arabic locale support for internationalization

[Copilot]

This PR adds support for two important languages that were missing from the mini_i18n library: Russian (ru) and Arabic (ar).

What's Added

🇷🇺 Russian (ru) Locale

• Complete Cyrillic script support with proper Russian translations
• Date formatting following Russian conventions: понедельник, 25 декабрь 2023 г. (full format)
• Short date format: 25.12.23 (DD.MM.YY)
• Number formatting with space as thousands separator and comma as decimal: 1 234,56
• Full Russian day and month names with proper abbreviations

🇸🇦 Arabic (ar) Locale

• Complete Arabic script support (RTL reading compatible)
• Date formatting in Arabic: الاثنين 25 ديسمبر 2023 (full format)
• Short date format: 25/12/23 (DD/MM/YY)
• Standard number formatting: 1,234.56
• Full Arabic day and month names with proper abbreviations

Example Usage

require 'mini_i18n'

date = Date.new(2024, 3, 15)
number = 1234.56

# Russian localization
MiniI18n.l(date, locale: :ru)     # => "пятница, 15 март 2024 г."
MiniI18n.l(number, locale: :ru)   # => "1 234,56"

# Arabic localization  
MiniI18n.l(date, locale: :ar)     # => "الجمعة 15 مارس 2024"
MiniI18n.l(number, locale: :ar)   # => "1,234.56"

Changes Made

• New files: Added lib/mini_i18n/locales/ru.yml and lib/mini_i18n/locales/ar.yml
• Documentation: Updated README.md to list the new supported languages
• Tests: Enhanced integration tests to cover the new locales
• Total languages: Expanded from 9 to 11 supported languages

The library now covers major world language families including Western European, East Asian, Slavic (Russian), and Semitic (Arabic) languages, providing comprehensive internationalization support for global applications.

All existing functionality remains unchanged and fully backward compatible.

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