Add ForbiddenError exception for 403 HTTP responses

[avokhmin]

Summary

Adds a new ForbiddenError exception class to properly handle HTTP 403 Forbidden responses from the ChargeBee API. This provides better error handling and allows applications to distinguish between forbidden access errors and other API errors.

Changes

Error Handling

• Added new ForbiddenError class that inherits from Error
• Enhanced handle_for_error method to detect and handle 403 status codes
• Provides clear error message: "Access forbidden. You do not have permission to access this resource."

Code Quality Improvements

• Renamed lib/chargebee/nativeRequest.rb → lib/chargebee/native_request.rb to follow Ruby naming conventions
• Refactored handle_for_error to return error objects instead of raising them inline (cleaner separation of concerns)
• Added YARD documentation for handle_for_error method

Testing

• Added comprehensive test coverage for 403 error scenarios

Motivation

When API keys lack permissions or access is restricted, the ChargeBee API returns a 403 status code. Previously, this was handled as a generic error, making it difficult for applications to distinguish permission issues from other error types. With ForbiddenError, applications can now:

• Catch and handle permission errors specifically
• Provide better user feedback about access issues
• Implement custom retry or fallback logic for authorization failures

Example Usage

begin
  ChargeBee::Customer.update(...)
rescue ChargeBee::ForbiddenError => e
  # Handle permission errors specifically
rescue ChargeBee::APIError => e
  # Handle other API errors
end