Port DateTimeOffset.ToUnixTimeMilliseconds to DateTime for much faster and efficent handling of Unix Time

DateTimeUnixTimeExtensions.cs

// DateTimeOffset first converts internally to DateTime, if you only want to get Unix Time you would need to do:
// DateTimeOffset.UtcNow.ToUnixTimeMilliseconds() which allocated more memory and is significantly slower due to
// embedding offset data based on the active timezone.
public static class DateTimeUnixTimeExtensions
{
    static readonly long UnixEpochTicks = DateTime.UnixEpoch.Ticks;
    static readonly long UnixEpochMilliseconds = UnixEpochTicks / TimeSpan.TicksPerMillisecond; // 62,135,596,800,000

    public static long ToUnixTimeMilliseconds(this DateTime instance)
    {
        return instance.Ticks / TimeSpan.TicksPerMillisecond - UnixEpochMilliseconds;
    }
}