ZonedDateTime class

Represents a date-time with timezone information.

This class combines a LocalDateTime with timezone information to represent a complete date-time with offset from UTC. Unlike Java's implementation, this version includes a built-in timezone database for common timezones without requiring external dependencies.

Key Features:

• Immutable: All operations return new instances
• Timezone Aware: Handles UTC offsets and common timezone names
• DST Support: Basic daylight saving time handling for major timezones
• Conversion: Easy conversion between timezones
• Formatting: ISO 8601 compliant string representation

Supported Timezone Formats:

• UTC Offsets: +05:00, -08:00, Z (for UTC)
• Timezone Names: EST, PST, GMT, CET, etc.
• Full Names: America/New_York, Europe/London, etc.

Usage Examples:

// Create from current time
final now = ZonedDateTime.now();
final nowInParis = ZonedDateTime.now(ZoneId.of('Europe/Paris'));

// Create with specific date-time
final localDT = LocalDateTime.of(2023, 12, 25, 15, 30);
final christmas = ZonedDateTime.of(localDT, ZoneId.of('America/New_York'));

// Parse from string
final parsed = ZonedDateTime.parse('2023-12-25T15:30:00+01:00[Europe/Paris]');

// Convert between timezones
final utc = christmas.toUtc();
final tokyo = christmas.withZoneSameInstant(ZoneId.of('Asia/Tokyo'));

// Arithmetic operations
final tomorrow = christmas.plusDays(1);
final nextHour = christmas.plusHours(1);

Timezone Database:

This implementation includes a comprehensive timezone database with:

• Major world timezones with their UTC offsets
• Daylight saving time rules for common timezones
• Historical timezone data for accurate conversions
• Support for both abbreviated and full timezone names