Upgrade Mailgun Webhooks Bundle to PHP 8.5, Symfony 7.4 and Symfony Mailer

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What changed

• upgrades the bundle to PHP 8.5, Symfony 7.4, Twig 3 and Doctrine ORM 3;
• declares the required curl, json and mailparse PHP extensions;
• migrates notification delivery from Swiftmailer to Symfony Mailer/Mime while preserving the existing service API;
• modernizes Doctrine persistence namespaces, configuration trees and PHPUnit tests;
• replaces the broken recursive subprocess retry command with bounded in-process retry behavior;
• adds GitHub Actions coverage for stable and lowest dependency sets.

Compatibility

The public notification methods continue to return 1 after a successful delivery and 0 when a throttled spam notification is intentionally skipped. Transport failures now propagate as Symfony Mailer exceptions instead of relying on Swiftmailer's failed-recipient array.

Validation

GitHub Actions runs Composer validation and PHPUnit on PHP 8.5 for stable and lowest supported dependencies. The branch still needs an application-level integration run together with the Azine.Me upgrade before release.