feat: support rolldown as an experimental engine

[XGHeaven]

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[Copilot]

Pull Request Overview

This PR adds experimental support for Rolldown as a new bundling engine alongside the existing Rollup and RSLib engines. The implementation includes engine detection, Rolldown-specific configuration options, and comprehensive test coverage.

• Add Rolldown as a new engine type with full configuration support
• Implement Rolldown bundling functionality with shared utilities from Rollup
• Add comprehensive integration tests for React components using Rolldown

Reviewed Changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/pkg/src/types.ts	Add 'rolldown' to EngineType union
packages/pkg/src/tasks/bundle.ts	Implement Rolldown build handling and fix bundle.write binding
packages/pkg/src/engine/rolldown/options.ts	New Rolldown options configuration using shared Rollup utilities
packages/pkg/src/engine/rollup/options.ts	Export shared utilities for use by Rolldown
packages/pkg/src/helpers/taskConfig.ts	Add bundle task assertion helper
packages/pkg/package.json	Add rolldown dependency
tests/helpers/run.ts	Fix test cleanup order and use serialize-javascript for config
tests/integration/react/*	Add React integration tests with Rolldown support
tests/integration/default/index.test.ts	Add Rolldown bundle test case

Files not reviewed (1)

• pnpm-lock.yaml: Language not supported

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[Copilot]

The TODO comment indicates incomplete implementation. The bundle.output should be properly typed and transformed to match the expected OutputResult interface instead of using any type assertions.

Suggested change

	return {
	taskName: context.buildTask.name,
	// TODO: correct type and value
	outputs: bundle.output as any,
	outputFiles: bundle.output as any,
	// Transform bundle.output to match OutputResult
	const outputs = Array.isArray(bundle.output)
	? bundle.output.filter((item) => item.type === 'chunk')
	: [];
	const outputFiles = Array.isArray(bundle.output)
	? bundle.output.filter((item) => item.type === 'asset')
	: [];
	return {
	taskName: context.buildTask.name,
	outputs,
	outputFiles,