Removes requests dependency and migrates fully to httpx

[mhajder]

Why

• Simplifies HTTP client code by consolidating on a single library
• Reduces dependency footprint and potential maintenance overhead
• Aligns with modern async-friendly HTTP client practices

What

• Eliminates all references to requests from source code, configuration, and tests
• Updates exception handling and mocks to use httpx types
• Removes requests from project dependencies and lock files

Benefits

• Consistency: Ensures all HTTP interactions use httpx, reducing confusion and duplication
• Modernization: Leverages httpx’s features, including async support and improved performance
• Maintenance: Streamlines dependency management and reduces risk from legacy libraries