Create Nylas v3 virtual calendars to schedule resources (rooms, equipment) without a real mailbox account

Steps

1. Create a virtual calendar connector, then a virtual account under that connector, before creating any virtual calendars.
2. POST /v3/grants/{grant_id}/calendars with a name and description to create the calendar under the virtual account's grant.
3. Note that the first virtual calendar created for a virtual account automatically becomes that account's primary calendar and cannot be changed later.
4. Reference the primary virtual calendar in subsequent event calls using the literal string "primary" instead of its calendar_id, consistent with how real provider calendars are addressed.
5. Use standard Events API calls (create/list/update) against the virtual calendar's grant_id/calendar_id exactly as you would for a real connected calendar, since virtual calendars share the same Events API surface.