🧪 [Testing] Add Comprehensive Unit Tests for Base HTTP Client

Description:

🚀 Overview

We need to build a robust test suite for our HTTPClient class in easyswitch/utils/http.py to ensure reliability across all mobile money API integrations.

*📋 Test Coverage Requirements

Core Functionality

• Initialization with different configurations
• Request methods (GET, POST, PUT, DELETE, PATCH)
• Header management and merging
• Timeout handling and retry mechanisms
• Error handling for network issues

Specific Scenarios

• File uploads with multipart/form-data
• JSON payload serialization
• Query parameters encoding
• Proxy configuration support
• Session management with context managers

Error Conditions

• HTTP error responses (4xx, 5xx)
• Network timeouts
• JSON parsing errors
• Rate limiting (429 responses)
• SSL/TLS certificate issues