iCalendar import: preserve ATTENDEE parameters

[eikopf]

Context

Per draft-ietf-calext-jscalendar-icalendar-22, the iCalendar ATTENDEE property has rich parameter data that maps to JSCalendar participants objects:

ATTENDEE Parameter	JSCalendar Participant Property
CN	name
CUTYPE	kind
DELEGATED-FROM	delegatedFrom
DELEGATED-TO	delegatedTo
EMAIL	email
MEMBER	memberOf
PARTSTAT	participationStatus
ROLE	roles
RSVP	expectReply
SENT-BY	sentBy

Current behaviour

The iCalendar import (crates/gnomon-import/src/lib.rs, lines 298–305) reduces each ATTENDEE to a bare calendar-address URI string:

if let Some(attendees) = $component.attendee() {
    let items: Vec<ImportValue> = attendees
        .iter()
        .map(|a| ImportValue::String(a.value.as_str().to_string()))
        .collect();
    if !items.is_empty() {
        $fields.push(("attendees", ImportValue::List(items)));
    }
}

All parameters (CN, PARTSTAT, ROLE, CUTYPE, RSVP, etc.) are silently lost.

Expected behaviour

Each ATTENDEE should be translated into a record preserving the available parameters so that downstream processing and JSCalendar export can reconstruct participant information.