refactor: reorganize zip module into smaller focused files

[shyim]

Extract code from the large zip.go file into focused modules:

• internal/archiver/: generic zip/unzip utilities
• cleanup.go: file cleanup and filtering logic
• checksum.go: XXH128 file checksumming
• packagist.go: Shopware version lookup via Packagist API

This improves code organization, testability, and makes the codebase easier to navigate.

[Copilot]

Pull request overview

This PR refactors the large zip.go file into smaller, more focused modules to improve code organization and testability. The refactoring extracts generic zip utilities, file cleanup logic, checksumming, and Packagist API integration into separate files while maintaining backward compatibility through proper function exports.

Changes:

• Extracted generic zip/unzip utilities to a new internal/archiver package with comprehensive test coverage
• Moved file cleanup and filtering logic to cleanup.go with dedicated test file
• Moved XXH128 checksumming functionality to checksum.go
• Extracted Shopware version lookup via Packagist API to packagist.go
• Added helper methods (ResolvePath, ResolveName) to ConfigExtraBundle for consistent path resolution
• Added shared helper function getShopwareVersionConstraintFromComposer to reduce code duplication between PlatformPlugin and ShopwareBundle
• Updated all references across the codebase to use the new package structure

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
internal/archiver/zip.go	New package containing generic zip/unzip utilities (Unzip, CreateZip, AddZipFiles)
internal/archiver/zip_test.go	Comprehensive tests for archiver package including zip slip security tests
internal/extension/cleanup.go	File cleanup and filtering logic extracted from zip.go
internal/extension/cleanup_test.go	Comprehensive tests for cleanup functionality
internal/extension/checksum.go	XXH128 checksumming logic for extension files
internal/extension/packagist.go	Shopware version lookup via Packagist API
internal/extension/config.go	Added ResolvePath and ResolveName helper methods to ConfigExtraBundle
internal/extension/root.go	Added shared getShopwareVersionConstraintFromComposer helper; updated to import archiver package
internal/extension/platform.go	Refactored to use shared getShopwareVersionConstraintFromComposer helper
internal/extension/bundle.go	Refactored to use shared getShopwareVersionConstraintFromComposer helper
internal/extension/validator_assets.go	Updated to use ConfigExtraBundle.ResolvePath helper
internal/extension/asset.go	Updated to use ConfigExtraBundle.ResolveName and ResolvePath helpers
internal/extension/git.go	Updated to import and use archiver.Unzip
internal/extension/zip.go	Significantly reduced by extracting code to focused modules
cmd/extension/extension_zip.go	Updated to use archiver.CreateZip
cmd/project/project_extension_upload.go	Updated to use archiver.AddZipFiles

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