Optimize shell initialization performance

[virtualzx-nad]

Original issue from nvm-sh/nvm nvm-sh#3410

The current shell initialization process, especially for zsh, is causing noticeable slowdown during shell startup.

Required improvements:

1. Profile and identify performance bottlenecks
2. Optimize version resolution logic
3. Reduce unnecessary file operations
4. Implement lazy loading where possible
5. Add benchmarking tests
6. Document performance improvements

Considerations:

• Maintain compatibility with existing features
• Handle edge cases properly
• Keep initialization reliable

This is a medium complexity task that requires understanding of:

• Shell scripting
• Performance optimization
• Zsh internals