feat: consume defaults in _config.yml

[cyjake]

fixes #19

[Copilot]

Pull Request Overview

This PR implements support for consuming defaults configuration from _config.yml, addressing issue #19. The implementation allows users to define default front matter values for pages and posts based on path and type scopes, following Jekyll's defaults pattern.

Key Changes

• Added getDefaults() function to apply default values from _config.yml to pages during the templating process
• Added type property to Post and Page parsers to enable type-based default matching
• Updated highlight.js API usage to accommodate breaking changes in v11
• Refactored test suite structure with new unit tests organized by functionality

Reviewed Changes

Copilot reviewed 16 out of 34 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
lib/writers/templated.js	Implements getDefaults() function for applying defaults from config; refactored to use async/await pattern and fs/promises
lib/parsers/post.js	Added type property to distinguish between 'posts' and 'drafts'
lib/parsers/page.js	Added type property set to 'pages'; fixed URL generation for markdown files
lib/highlight.js	Updated highlight.js API call from old highlight(lang, code) to new highlight(code, { language }) format
test/unit/site.test.js	New unit tests for Site class, including test coverage for defaults feature
test/unit/parsers/post.test.js	New unit tests for post parsing functionality
test/unit/parsers/page.test.js	New unit tests for page parsing functionality
test/unit/writers/templated.test.js	New unit tests for templated writer
test/unit/liquid.test.js	Updated import path to match new test directory structure
test/site.test.js	Removed old test file as functionality moved to unit tests
test/fixture/defaults/*	New test fixture demonstrating defaults feature with layouts and scoped defaults
test/fixture/basic/*	New basic test fixture for core functionality testing
package.json	Updated test script to run tests recursively

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[Copilot]

@cyjake I've opened a new pull request, #26, to work on those changes. Once the pull request is ready, I'll request review from you.