Add uv package manager support

[Daucloud]

Add uv package manager support

Summary

This PR adds support for the uv Python package manager to oh-my-tuna, enabling automatic configuration of TUNA PyPI mirrors for uv users.

What's Added

• New UV class: Implements the Base interface to support uv package manager
• Configuration management: Automatically configures uv to use TUNA PyPI mirror (https://mirrors.tuna.tsinghua.edu.cn/pypi/web/simple/)
• Cross-platform support: Works with both user-level (~/.config/uv/uv.toml) and system-level (/etc/uv/uv.toml) configurations
• Global/local mode support: Respects the -g/--global flag for system-wide or user-specific configurations

Key Features

• Detection: Automatically detects if uv is installed via uv --version
• Status checking: Verifies if TUNA mirror is already configured
• Activation: Creates proper TOML configuration with TUNA mirror as default index
• Deactivation: Cleanly removes configuration files when disabling
• Directory creation: Automatically creates config directories if they don't exist

Configuration Format

The implementation generates a clean TOML configuration:

[[index]]
url = "https://mirrors.tuna.tsinghua.edu.cn/pypi/web/simple/"
default = true

Testing

• Works in both global (-g) and local modes
• Properly handles missing configuration directories
• Safe file operations with appropriate error handling
• Integrates seamlessly with existing oh-my-tuna workflow

Usage

# Activate uv mirror (user-level)
python oh-my-tuna.py up

# Activate uv mirror (system-level)  
python oh-my-tuna.py up -g

# Check status
python oh-my-tuna.py status

# Deactivate
python oh-my-tuna.py down

This enhancement brings uv support in line with other package managers already supported by oh-my-tuna, providing a consistent experience for Python developers using this modern package manager.