v2.0.0 - PHP 8.3+ and Dependency Upgrades

Breaking Changes

• Minimum PHP version raised to 8.3
• PublisherTokenProvider and SubscriberTokenProvider now require a
  secret key of at least 32 characters (256 bits). Passing a shorter
  key will throw InvalidSecretKeyLengthException. This is enforced to
  comply with the HMAC-SHA256 specification required by lcobucci/jwt v5.

Added

• InvalidSecretKeyLengthException to enforce HMAC-SHA256 minimum key
  length requirement
• PHP 8.3 and 8.5 added to CI test matrix (unit and functional)

Changed

• Bumped lcobucci/jwt from ^4.1.5 to ^5.6
• Bumped nyholm/psr7 from ^1.4.1 to ^1.8
• Bumped phpstan/phpstan from ^0.12 to ^1.0
• Bumped phpunit/phpunit from ^8.0 to ^11.0
• Bumped symfony/http-client from ^5.3 to ^6.0
• All properties now use typed declarations
• PHPUnit test annotations migrated from @test docblocks to #[Test]
  attributes
• PHPUnit XML configuration migrated to new schema

Fixed

• Missing declare(strict_types=1) in TokenProviderInterface
• $topics property in NotificationBuilder now explicitly initialized
  to empty array