…h Symfony Mailer

  BREAKING CHANGES:
  - Minimum PHP version raised from 5.6 to 8.2
  - SwiftMailer replaced with Symfony Mailer
  - Helper constructor signature: ?MailerInterface instead of ?\Swift_Mailer
  - Helper::sendMail() returns Symfony\Component\Mime\Email instead of Swift_Message
  - SerializableClosure wrapper no longer supported (pass raw closures directly)

  ## Dependency Updates

  - php: ^8.2
  - symfony/mailer: ^6.4|^7.0|^8.0 (new, replaces swiftmailer/swiftmailer)
  - symfony/process: ^6.4|^7.0|^8.0
  - symfony/filesystem: ^6.4|^7.0|^8.0 (dev)
  - dragonmantank/cron-expression: ^3.6
  - opis/closure: ^3.6|^4.0
  - phpunit/phpunit: ^10.5|^11.0 (dev)

  Removed:
  - swiftmailer/swiftmailer (abandoned)
  - mp091689/dump-die (dev dependency)

  ## Core Changes

  ### src/Helper.php
  - Complete mailer rewrite using Symfony Mailer
  - New buildMailerDsn() method converts config to Symfony DSN format
  - SMTP security mapping preserved from SwiftMailer behavior:
    - 'ssl' → smtps:// (implicit TLS, port 465)
    - 'tls' → smtp:// (STARTTLS auto-negotiated, port 587)
    - null → smtp:// (plain or STARTTLS if available)
  - Credentials properly URL-encoded for special characters

  ### src/Jobby.php
  - Opis Closure 4.x compatibility: use serialize() function instead of
    SerializableClosure class (which now has private constructor)
  - Modernized array destructuring syntax

  ### src/BackgroundJob.php
  - Opis Closure 4.x compatibility: use unserialize() function
  - PHP 8.2+ constructor property promotion
  - Fixed implicit nullable parameter deprecation

  ### src/ScheduleChecker.php
  - CronExpression::factory() replaced with direct instantiation
  - PHP 8.2+ constructor property promotion
  - Fixed implicit nullable parameter deprecation

  ## Test Updates

  All test files migrated to PHPUnit 10/11:
  - setUp()/tearDown() return type declarations
  - @ExpectedException annotations → expectException() method calls
  - assertContains() for strings → assertStringContainsString()
  - assertInternalType() → assertIsArray(), assertIsString(), etc.
  - Static data providers (PHP 8.1+ requirement)

  ### tests/HelperTest.php
  - Mailer tests updated for Symfony Mailer mock (MailerInterface)
  - Added 7 parameterized DSN building tests covering:
    - sendmail, mail (native), smtp plain
    - smtp with auth, smtp with TLS, smtps with SSL
    - Special characters in credentials

  ### tests/BackgroundJobTest.php
  - Restored meaningful closure test (built-in function calls)
  - Updated mock setup for new Helper interface

  ### tests/JobbyTest.php
  - Added Opis Closure function imports
  - Verified closure serialization roundtrip

  ## Configuration

  ### phpunit.xml
  - Updated to PHPUnit 10+ schema
  - Replaced <filter><whitelist> with <source><include>
  - Added cacheDirectory for test performance

  ### .github/workflows/tests.yml (new)
  - CI matrix: PHP 8.2, 8.3, 8.4
  - Symfony version matrix: 6.4, 7.0, 8.0
  - Excludes PHP 8.2/8.3 with Symfony 8.0 (requires 8.4+)

  ## Documentation

  ### UPGRADE-3.0.md (new)
  - Complete migration guide for users upgrading from 2.x
  - SMTP security behavior documentation
  - Code examples for Helper class extension
  - Migration checklist

  ### README.md
  - Updated requirements section
  - Fork notice and attribution
  - Reference to upgrade guide

  ## Verification

  - 70 tests, 96 assertions, all passing
  - 5 skipped (platform-specific tests)
  - Tested on PHP 8.4.16
  - Full closure serialization flow verified
  - All SMTP DSN configurations verified

  BREAKING CHANGES:
  - Minimum PHP version increased from 8.2 to 8.3
  - PHPUnit requirement changed from ^10.5|^11.0 to ^12.0

  Changes:
  - Update composer.json PHP requirement to ^8.3
  - Update composer.json PHPUnit requirement to ^12.0
  - Add PHP 8.5 to CI test matrix
  - Convert PHPUnit annotations to PHP 8 attributes across all test files
  - Fix PHP 8.5 strict typing: cast getmypid() to string for fwrite()
  - Fix PHP 8.5 strict typing: add null check before is_file() call
  - Add explicit return type string|false to BackgroundJob::getLogfile()
  - Add UPGRADE-4.0.md migration guide

  Introduce Jobby\Mailer\MailerInterface to decouple job failure
  notifications from Symfony Mailer, allowing users to implement
  custom mailers (PHPMailer, native mail(), etc.).

  New components:
  - MailerInterface: defines send() contract for notifications
  - SymfonyMailerAdapter: default implementation using Symfony Mailer
  - NullMailer: no-op implementation for testing with mail recording

  Changes to Helper:
  - Constructor accepts MailerInterface|SymfonyMailerInterface|null
  - sendMail() now returns void instead of Email (BREAKING)
  - Email building logic moved to SymfonyMailerAdapter

  BREAKING CHANGE: Helper::sendMail() return type changed from Email
  to void. Test code asserting on the returned Email object must be
  updated to use NullMailer or mock MailerInterface instead.