Israel - add new country support

[xdebbie]

Summary

• Add holiday provider for Israel (IL) with support for Hebrew calendar-based holidays
• Register Israel in HolidaySystem.cs

Holidays Included

Public Holidays:

• Rosh Hashanah (Jewish New Year) - 2 days
• Yom Kippur (Day of Atonement)
• Sukkot (First day)
• Shemini Atzeret / Simchat Torah
• Passover (First and Seventh days)
• Independence Day (Yom Ha'atzmaut)
• Shavuot

Observances & Optional Holidays:

• Purim
• Holocaust Remembrance Day (Yom HaShoah)
• Memorial Day (Yom HaZikaron)
• Jerusalem Day
• Hanukkah (8 days)
• Chol HaMoed (intermediate days for Passover and Sukkot)
• Holiday eves (half-day bank holidays)

Implementation Notes

• Uses .NET HebrewCalendar for accurate Hebrew-to-Gregorian date conversion
• Handles leap years (Purim in Adar II)
• Implements date adjustments per Israeli law when holidays fall near Shabbat

Test plan

• Verify holidays render correctly for multiple years
• Verify Hebrew calendar date conversions are accurate