feat: implement enforce-tfunction-type ESLint rule

[tupe12334]

Summary

• Implements new ESLint rule enforce-tfunction-type to enforce usage of official TFunction type from i18next
• Replaces custom translation function types with the official TFunction type for better type consistency

Features

• Auto-detection: Identifies TypeScript type aliases, interfaces, and inline type annotations that match TFunction signatures
• Auto-fix: Automatically replaces custom types with TFunction and manages i18next imports
• Import management: Creates new i18next imports or extends existing ones as needed
• Parameter flexibility: Supports multiple parameter names (key, translationKey, i18nKey)
• Comprehensive testing: 23 test cases covering valid/invalid scenarios and edge cases

Implementation Details

• Detects function signatures like (key: string) => string and similar patterns
• Handles TypeScript type aliases, interface call signatures, and variable type annotations
• Provides helpful error messages with auto-fix suggestions
• Follows repository coding standards and testing patterns

Test Coverage

• 23 total tests across 2 test files (default.js and edge-cases.js)
• Fixture-based testing with TypeScript parser integration
• Edge case coverage including complex signatures and import scenarios
• Full test suite integration - all existing tests still pass

Files Changed

• lib/rules/enforce-tfunction-type.js - Main rule implementation
• tests/lib/rules/enforce-tfunction-type/ - Comprehensive test suite
• tests/lib/fixtures/enforce-tfunction-type/ - Test fixtures
• package.json - Updated test script to include new rule tests

Resolves #146

🤖 Generated with Claude Code