# ZonedDateTime.fromDateTime constructor

ZonedDateTime.fromDateTime(

1. DateTime dateTime, [
2. ZoneId? zone

])

Creates a ZonedDateTime from a standard DateTime object.

The DateTime is assumed to be in the specified timezone. If no timezone is provided, it defaults to UTC.

Example:

    final dateTime = DateTime(2023, 12, 25, 15, 30);
    final zonedUtc = ZonedDateTime.fromDateTime(dateTime); // Assumes UTC
    final zonedEst = ZonedDateTime.fromDateTime(dateTime, ZoneId.of('EST'));

    print('As UTC: $zonedUtc');
    print('As EST: $zonedEst');

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

## Implementation

    factory ZonedDateTime.fromDateTime(DateTime dateTime, [ZoneId? zone]) {
      zone ??= ZoneId.UTC;
      final localDateTime = LocalDateTime.fromDateTime(dateTime);
      return ZonedDateTime.of(localDateTime, zone);
    }