listAttachments follows Graph pagination and normalizes file, item, and
reference attachments. File contents are decoded when Graph includes them.
automations/list-outlook-attachments.automation.ts
messageId is required. Optional limit defaults to 100 and permits 1–10,000
across pages. Optional account selects the binding.
Returns attachments with attachmentId, name, type (file, item,
reference, or unknown), size, isInline, optional content ID, content
location and MIME type, and optional decoded file: File. file can be absent
for metadata-only, item, and reference attachments. Use getAttachment when you
need one attachment’s contents.