an interface to most facets of the [Fastly API](https://developer.fastly.com/reference/api).

Changes for 4.01 - 2023-07-12

• fix(billing): rename response field 'lines' to 'line_items'.
• fix(billing): restructure response models like 'aria_invoice_id'.
• fix(billing): make 'sent_at', 'locked', 'require_new_password', 'two_factor_auth_enabled' nullable.