refactor(types): align attachment types with monorepo public-api

[lucasfcosta]

This PR mostly refactors the types for the Node SDK so they align more closely with the API and so that there's less repetition:

• Rename Attachment → AttachmentData and add JSDoc with correct endpoint paths
• Remove redundant ListAttachmentsApiResponse (duplicate of ListAttachmentsResponseSuccess)
• Extract InboundAttachment interface for raw DB metadata in GET /inbounds/{id}
• Fix GetReceivingEmailResponseSuccess: headers is nullable, raw is optional

My request for reviewers: can you double check if I missed anything comparing this to the API? I compared myself and it looks correct, but given we're iterating on this it would be worth a second pass.

Important note: the types are indeed not equal. That's because inbound attachments that appear on the list don't get a download URL (that's intended) and we cannot make both the inbound and outbound type 100% equal due to breaking changes that would be needed.

---

Summary by cubic

Refactors attachment types to match the public API and clearly separate signed-URL attachments from inbound metadata. This reduces duplication and fixes mismatches in the receiving email response.

• Refactors
  • Renamed Attachment to AttachmentData with JSDoc for signed-URL endpoints.
  • Removed ListAttachmentsApiResponse; use ListAttachmentsResponseSuccess for sending and receiving lists.
  • Added InboundAttachment for GET /inbounds/{id} (raw DB metadata, nullable fields).
  • Fixed GetReceivingEmailResponseSuccess: headers can be null; raw is optional and can be null.
  • Updated list/get attachment types, exports, and tests.

^{Written for commit d695be8. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 10 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.