All models used in the GrowERP flutter frontend

The base package all other growerp_* building blocks depend on. Provides:

• Data models (@freezed + json_serializable) for every entity used across GrowERP (party/company/user, catalog, inventory, orders/invoices/accounting, activities, marketing/outreach, ADK agents, website/wiki, manufacturing, rental, etc.)
• RestClient — the retrofit-generated REST client for the Moqui backend
• JSON converters and CSV export helpers shared by every building block

Please see https://www.growerp.com for documentation.