feat: implement PKPassBundle

[tschoffelen]

Implements a new class called PKPassBundle, which allows you to package multiple passes together and present them at once in Safari:

You can use it like this:

use PKPass\PKPassBundle;

$bundle = new PKPassBundle();
$bundle->add($pass1);
$bundle->add($pass2);

$bundle->output();

Fixes #153

[Copilot]

Pull Request Overview

This PR introduces the new PKPassBundle class with associated tests, examples, and documentation to bundle multiple passes into a single .pkpasses file for Safari download. Key changes include the implementation of the PKPassBundle class with ZIP archive functionality, comprehensive PHPUnit tests to validate bundle behavior, and updated documentation and example usage.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
tests/PKPassBundleTest.php	Added tests for creating, saving, and naming a pass bundle
src/PKPassBundle.php	Implemented the PKPassBundle class with ZIP archive creation/output
examples/bundle.php	Provided an example of creating and outputting a pass bundle
docs/PKPassBundle.md	Updated documentation covering the API, usage examples, and error handling