Updated FormatDatetime event timezones

Property	Value
description	Added preferred event datetime fields and timezone-aware datetime attributes.
version	1.0.2
type	Update
related	MAC Core, Format Datetime

• Updated the built-in event preset to prefer event_start and event_end.
• Preserved event_start_datetime and event_end_datetime as fallback aliases for existing builds.
• Kept the existing separate event_start_date, event_end_date, event_start_time, and event_end_time fields supported.
• Added IANA timezone handling for event_timezone, including ACF choice-array values.
• Used the WordPress site timezone when the event timezone is missing, blank, or invalid.
• Updated attr and HTML <time datetime=""> output so time-bearing values include a timezone offset and date-only values stay date-only.
• Added regression coverage for alias precedence, timezone fallback, date-only attributes, and HTML datetime attributes.