Add refresh token fields to Session.copy_attributes_from

Prevents sessions from losing refresh token data during copy operations, which would break token refresh functionality.

Fixed merge conflict resolution: After merging main's refactored copy_attributes_from (direct assignment instead of JSON.parse), the new refresh_token fields were inadvertently omitted.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: lizkenyon

lib/shopify_api/auth/session.rb

@@ -151,6 +151,8 @@ def copy_attributes_from(other)
         @associated_user = other.associated_user
         @is_online = other.online?
         @shopify_session_id = other.shopify_session_id
+        @refresh_token = other.refresh_token
+        @refresh_token_expires = other.refresh_token_expires
         self
       end