fix(tools): make version optional and improve error reporting for install-vscode

[ChronosMasterOfAllTime]

Summary

Improves the goenv tools install-vscode command by making the version argument optional and enhancing error reporting during tool installation.

Changes

User Experience Improvements

• Optional version argument: Now defaults to the current Go version when not specified
  • Before: goenv tools install-vscode <version> (required)
  • After: goenv tools install-vscode [version] (optional)
• Auto-detection: Automatically uses GetCurrentVersionResolved() to handle partial versions
• Better examples: Reorganized help text to show the most common use case first

Error Reporting Enhancements

• Stderr capture: Captures and displays error output from failed tool installations
• First error context: Preserves the first error encountered for better debugging
• Mode-aware output: Respects verbose/non-verbose mode settings
  • Verbose: Shows all output in real-time
  • Non-verbose: Shows clean status with detailed errors only on failure

Bug Fixes

• Fixed gotests package path: Corrected from github.com/cweill/gotests to github.com/cweill/gotests/gotests

Testing

Manually tested:

• ✅ Installation with explicit version: goenv tools install-vscode 1.25.2
• ✅ Installation with current version: goenv tools install-vscode
• ✅ Error handling when no version is set
• ✅ Error reporting for failed tool installations
• ✅ Verbose and non-verbose output modes

Example Usage

# Install VSCode tools for current version (new!)
goenv tools install-vscode

# Install VSCode tools for specific version
goenv tools install-vscode 1.25.2

# Show what would be installed
goenv tools install-vscode --dry-run

Related Issues

This PR improves the usability of the VS Code integration by reducing friction in the most common use case (installing tools for the current version).