Webhook implementation

[eddyjaga]

This pull request introduces a major new feature: a complete, production-ready webhook management system for the Zai Payment gem. It adds full CRUD support for webhooks, a reusable API client, standardized response and error handling, comprehensive documentation, and a full test suite. The infrastructure is designed for easy extension to future resources.

New Webhook API and Core Infrastructure:

• Added lib/zai_payment/resources/webhook.rb with full CRUD operations for webhooks, including input validation, error handling, and pagination support.
• Introduced lib/zai_payment/client.rb (base HTTP client) and lib/zai_payment/response.rb (response wrapper) for reusable, thread-safe API communication and standardized response handling.

Enhanced Error Handling:

• Updated lib/zai_payment/errors.rb to include new error classes for all major API scenarios (validation, authentication, not found, rate limit, network, server errors, etc.).

Documentation and Examples:

• Added comprehensive documentation in docs/WEBHOOKS.md, usage examples in examples/webhooks.rb, and updated the README.md and CHANGELOG.md to reflect new features and usage patterns. [1] [2] [3]

Testing:

• Added a new test suite in spec/zai_payment/resources/webhook_spec.rb covering all webhook operations and error scenarios. [1] [2]

Configuration and Versioning:

• Updated lib/zai_payment.rb to expose the new webhooks resource and bumped the gem version to 1.1.0.

These changes ensure a clean, extensible, and well-documented foundation for future API resources, following Ruby best practices and providing robust error handling and test coverage.