test: Add comprehensive CLI interface testing with action objects

[Copilot]

This PR implements comprehensive testing for the CLI interface by refactoring the command structure to use testable action objects and factory functions.

Changes Made

1. Action Interface Design

Created typed action interfaces that define handlers for each CLI command:

interface CacheActions {
  onRoot(options: object, command: Command): Promise<void>
  onPath(options: object, command: Command): Promise<void>
  onPrune(options: object, command: Command): Promise<void>
  onDelete(version: string, options: object, command: Command): Promise<void>
}

interface RootActions {
  onTargets(targets: string[], options: { verbose?: boolean; dependencies?: boolean }, command: Command): Promise<void>
}

2. Command Factory Functions

Implemented factory functions that accept action objects and return configured Commander.js commands:

• createRootCommand(actions: RootActions) - Creates the main CLI command
• createCacheCommand(actions: CacheActions) - Creates the cache management subcommand

3. Refactored CLI Implementation

Updated cli.ts to use the factory pattern while preserving all existing functionality:

• Extracted command handlers into action implementations
• Maintained identical console output and behavior
• Preserved TypeScript version checking functionality

4. Comprehensive Test Suite

Added 8 test cases using Vitest spies to verify:

• Command configuration (names, descriptions, options)
• Action handler calls with correct arguments and signatures
• Integration between root and cache commands
• Various argument combinations and flag handling

Verification

The refactoring maintains 100% backward compatibility:

• All CLI commands work identically to before
• Console output remains unchanged
• TypeScript checking functionality preserved
• All existing and new tests pass (13/13)

Example usage remains the same:

# Root command functionality unchanged
mtsv file.d.ts --verbose
mtsv --dependencies

# Cache commands work identically  
mtsv cache
mtsv cache path
mtsv cache prune
mtsv cache delete 5.0.0

The CLI interface is now fully testable with mock actions while maintaining complete functional compatibility.

Fixes #9.

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