Add billing provider packages for PayPal, Braintree, and Authorize.Net

[cobycloud]

Summary

• add a swarmauri_billing_paypal package with stubbed provider implementation, packaging metadata, and documentation
• add a swarmauri_billing_braintree package covering checkout, risk, and webhook features plus README and build config
• add a swarmauri_billing_authorize_net package focused on transactions/refunds with docs and metadata
• register the new billing packages in the uv workspace configuration

Testing

• uv run --directory . --package swarmauri_billing_paypal ruff format .
• uv run --directory . --package swarmauri_billing_paypal ruff check . --fix
• uv run --directory . --package swarmauri_billing_braintree ruff format .
• uv run --directory . --package swarmauri_billing_braintree ruff check . --fix
• uv run --directory . --package swarmauri_billing_authorize_net ruff format .
• uv run --directory . --package swarmauri_billing_authorize_net ruff check . --fix

---

https://chatgpt.com/codex/tasks/task_e_68f0bd510cb4832683889cfb3c87ba08