Creates and saves a new address entry in the user's address book. Saved addresses can be quickly reused when creating shipments, eliminating the need to re-enter full address details each time.

When to use: Call this endpoint when a user wants to store a frequently used origin or destination address for future shipments, or when onboarding a new customer whose address should be saved for repeat orders.

Prerequisites:

• Valid JWT token in the Authorization header
• A user_id identifying the address owner
• A complete address object with required fields: name, street, city, state, zipcode, and country

Key behaviors:

• Returns the newly created address_id which can be referenced in future shipment creation calls
• The country field must be a valid two-letter ISO country code (e.g., MX, US, CO)
• Optional fields include company, street2, and phone
• Duplicate addresses are not automatically detected; the same address can be saved multiple times
• Saved addresses can be retrieved with GET /all-addresses and managed with PUT /user-address/{address_id} or DELETE /user-address/{address_id}