fix(emails): make filename and content_disposition nullable in EmailAttachment types

[dielduarte]

open api spec updated here: resend/resend-openapi#64

Summary by cubic

Make filename and content_disposition nullable in received email attachment types to match API responses and avoid type errors. Applies to EmailAttachment and EmailAttachmentDetails in resend/emails/_received_email.py and addresses DEV-609.

• Bug Fixes
  • Changed filename and content_disposition from str to Optional[str] in EmailAttachment and EmailAttachmentDetails.
  • Aligns Python types with cases where these fields are null in real emails.

^{Written for commit e4e9b27. Summary will update on new commits.}

[gabrielmfern]

good to ask @drish for a review here too

[cubic-dev-ai]

cubic analysis

No issues found across 1 file

Confidence score: 5/5

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

Linked issue analysis

Linked issue: DEV-609: received email attachment types in python

Status	Acceptance criteria	Notes
✅	Make filename nullable (Optional[str]) in EmailAttachment and EmailAttachmentDetails	Diff changes the filename field type to Optional[str] in both EmailAttachment and EmailAttachmentDetails TypedDicts.
✅	Make content_disposition nullable (Optional[str]) in EmailAttachment and EmailAttachmentDetails	Diff changes the content_disposition field type to Optional[str] in both EmailAttachment and EmailAttachmentDetails TypedDicts.

_{Auto-approved: This change only updates two type annotations from str to Optional[str] in EmailAttachment and EmailAttachmentDetails TypedDicts, aligning with the API spec where filename and content_disposition can be null, with no impact on runtime logic or broader system behavior.}