Macos support

[hi2code]

Add macOS Support with Homebrew Integration

Summary

This PR adds comprehensive macOS support to PVM (PHP Version Manager) by integrating with Homebrew for PHP installation and management.

Changes

• macOS Support: Added platform detection and dedicated installation logic for macOS
• Homebrew Integration: Uses Homebrew to install PHP versions, including support for older versions via shivammathur/php tap
• Cross-Platform: Maintains existing Windows support while adding macOS compatibility
• Documentation: Updated README to include macOS installation instructions

Key Features

• Automatic Homebrew detection and validation
• Support for installing PHP versions using brew install php@version
• Integration with shivammathur/php tap for older PHP versions (7.x and below)
• Proper version management and switching capabilities
• Added uninstall command for better version management

Installation

Users can now install PVM on macOS using:

go install github.com/hjbdev/pvm@latest

Then use pvm install <version> to install PHP versions via Homebrew.

Testing

Tested on macOS and Windows with various PHP versions to ensure proper installation and switching functionality.