feat(api)!: add carrier delivery estimate; nullable trust grantor fields

[increase-releases]

This spec sync updates the check transfers and entities resources.

• Add carrier_estimated_delivery_at to the check transfer physical check tracking update, indicating when the carrier expects the check to be delivered.
• Make the trust grantor's address and date_of_birth nullable on the Entity response.
• Clarify trust grantor documentation ("person's" → "grantor's").

Held for manual review — breaking change: existing trust grantor response fields address and date_of_birth are now nullable, which can break callers that read them as non-null.

BREAKING CHANGE: trust grantor address and date_of_birth on the Entity response are now nullable.

Spec: f6a1f4bde6efb971145f60df61c0f8cc.