Refactor: Clean API design & enhanced file upload support

[2-seo]

🎯 Overview

Refactor FastHTTP to provide a cleaner API design and enhanced file upload support.

✨ Improvements

API Simplification

• Rename serialize_object → to_dict for clarity
• Remove unnecessary is_serializable from public API
• Streamline exports: only FastHTTP & to_dict exposed

Enhanced File Upload

• Add file object detection (io.IOBase)
• Preserve file objects during serialization
• Support mixed form data (objects + files)

Architecture

• Create dedicated fasthttp.serializers module
• Separate serialization logic from HTTP client
• Improve type hints with TypeAlias

🔧 Technical Details

• Zero external dependencies maintained
• Recursive object serialization
• Backward-compatible behavior
• Clean modular design

📦 Target Version

0.1.1