Add full Italian (it) locale support

[Pixsd]

Summary

This PR adds full Italian language support to chrono-node. Italian locale is based on the English locale structure.

Changes

• Added new Italian locale (src/locales/it/) with:
  • 14 parsers: casual date/time, weekday, month name, relative dates, time expressions, time units (ago/later/within), slash format, year-month-day
  • 6 refiners: date-time merging, date range merging, year suffix extraction, relative date merging, unlikely format filtering
  • Constants: Italian weekdays, months, ordinal numbers, time units
  • Configuration: strict and casual parsing modes

Supported expressions

Examples of Italian phrases now recognized:

• domani alle 15:00 → tomorrow at 3pm
• lunedì prossimo → next Monday
• il 25 dicembre 2025 → December 25, 2025
• tra 2 settimane → in 2 weeks
• 3 giorni fa → 3 days ago
• il mese prossimo → next month
• venerdì scorso alle 18:00 → last Friday at 6pm
• stamattina / stasera → this morning / this evening
• dopodomani / l'altro ieri → day after tomorrow / day before yesterday
• un anno e 1 mese fa → 1 year and 1 month ago

Tests

• Added 20 test files covering all parsers and refiners
• All 61 tests passing

Exports

• chrono.it - casual parsing (default)
• chrono.it.strict - strict parsing mode