feat: add comprehensive test suite with Jest

[tinsever]

• Add Jest test framework with 127 passing tests
• Add test coverage for all library modules:
  • cache.js (100% coverage)
  • noop.js (100% coverage)
  • google-font-list.js (93% coverage)
  • request.js (93% coverage)
  • google-font.js
  • system-font.js
• Add jest.config.js with coverage configuration
• Add test scripts: test, test:watch, test:coverage

[Copilot]

Pull request overview

This PR adds a comprehensive Jest testing framework to the project with 127 passing tests covering all library modules. The test suite provides excellent coverage across cache, request, google-font, google-font-list, system-font, and noop modules, with most modules achieving 93-100% coverage.

Key Changes

• Added Jest 30.2.0 as a dev dependency with test, test:watch, and test:coverage scripts
• Created 6 test files covering all major library modules with comprehensive unit tests
• Added jest.config.js with coverage configuration excluding Windows-specific code
• Removed test/ from .gitignore to allow test files to be committed

Reviewed changes

Copilot reviewed 7 out of 10 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
test/system-font.test.js	Comprehensive tests for SystemFont module including file operations, folder validation, and platform-specific installation paths
test/request.test.js	Tests for HTTP/HTTPS request handling, redirects, error handling, streaming functionality, and timeout behavior
test/noop.test.js	Simple but thorough tests for the noop utility function's error handling behavior
test/google-font.test.js	Tests for GoogleFont class including constructor, variant normalization, URL generation, and API methods
test/google-font-list.test.js	Extensive tests for font list operations including searching, filtering, cloning, and data population
test/cache.test.js	Tests for cache read/write operations, TTL validation, and error handling
package.json	Added test scripts and Jest as a dev dependency
jest.config.js	Jest configuration with node environment, coverage settings, and test pattern matching
.gitignore	Removed test/ directory exclusion to allow committing test files, added *.tar.gz

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