Enhance documentation and testing framework for phpvm

- Updated CLAUDE.md to provide clearer guidance on development practices and testing procedures.
- Expanded README.md with detailed descriptions of built-in testing, GitHub Actions workflows, and testing coverage across platforms.
- Improved phpvm.sh with enhanced OS detection, PHP version validation, and installation logic for various package managers.
- Added comprehensive system information output for debugging purposes.
- Implemented caching for command availability checks to optimize performance.
- Enhanced error handling and user feedback during PHP installation and version switching.
- Introduced new functions for finding .phpvmrc files and auto-switching PHP versions based on their contents.

Author: Thavarshan