Add support for pre-request and post-request scripts

[virtualzx-nad]

Original issue: httpie#1454

Problem:
Users need the ability to run custom scripts before and after HTTP requests for request modification and response processing.

Requirements:

1. Add support for pre-request script execution
2. Add support for post-request script execution
3. Define script API and environment
4. Handle script errors gracefully
5. Include security considerations
6. Add documentation and examples

Difficulty: Moderate
Type: Feature