Feature Request: full country name available in list & segment exports

🔍 Problem Statement
As an admin, I experience list and segment exports containing only a 2-letter country code, which is incompatible with USPS and postal systems that require the full country name on address labels.

💡 User Story
As an admin, I want list and segment exports to include the full country name, so that I can use the export directly for mailing without manual post-processing.

🎯 Definition of Done
- Given a list or segment export, when downloaded, then the country column includes the full country name (e.g., "Canada" instead of "CA").
- This change impacts the API (list/segment export endpoints).
- Limitations: ISO 3166-1 names are used; country code column is retained for backwards compatibility.

Problem: Only the country code is available when exporting single lists or segments. USPS requires the full country name spelled out on an address label and will not accept only the country code. To resolve this, we have to manually add in the full country name after exporting. Example: To ship to Canada, the label must say “Canada” at the end of the address and not “CA” Solution: add the full country name column back into the list and the segments exports so that no manual manipulation is needed in order to use the lists and segments to create address labels. This feature is currently available from the fulfillment export, but not all of our lists get added to a fulfillment.