Add Messenger assertions

[TavoNiievez]

What

Adds a MessengerAssertionsTrait so functional tests can assert against Symfony Messenger, which until now had no coverage in this module — even though its Messenger-based siblings (Mailer, Notifier) are fully covered.

New $I-> steps:

Step	Purpose
seeMessageDispatched(string $messageClass, ?string $bus = null)	a message of the given class was dispatched (optionally per bus)
dontSeeMessageDispatched(string $messageClass, ?string $bus = null)	no message of the given class was dispatched
seeDispatchedMessageCount(int $expectedCount, ?string $bus = null)	exact number of dispatched messages (optionally per bus)
grabDispatchedMessageClasses(?string $bus = null)	the dispatched message class names, in dispatch order

These follow the module's naming convention: see*/dontSee* for module-native assertions (no upstream Symfony web-test equivalent, so not assert*), grab* for getters. grabDispatchedMessageClasses() returns class-strings — hence the explicit name, distinct from the object-returning grabSentEmails/grabSentNotifications.

How

Reads Symfony's messenger profiler data collector via the existing grabCollector() helper — the same pattern the Events/Form/Twig traits use. Wires the messenger collector into DataCollectorName and the grabCollector() conditional return-type map.

The collector stores cloned VarDumper snapshots (message class, bus, exceptions), not live message objects, so payload-level assertions are intentionally out of scope. The class-name reader narrows the Data tree to the message.type leaf via ArrayAccess rather than recursively materializing each entry's whole snapshot (message payload, stamps, caller, exception trace) — handling both the plain-string type (Symfony ≤ 7.x) and the ClassStub representation (8.x).

Tests

Adds a self-contained Messenger setup to the test app (framework.messenger default bus + a sample message, handler, controller action and route) and tests/MessengerAssertionsTest.php covering counts, per-bus filtering, positive/negative dispatch checks and the no-dispatch case. Passes phpunit, phpstan (level max) and cs-check.

Note: enabling framework.messenger routes Mailer through the bus by default, so the test app sets mailer.message_bus: false to keep mail synchronous.

Functional tests

Per CONTRIBUTING.md, the matching functional tests are submitted as companion PRs to Codeception/symfony-module-tests (branches 5.4, 6.4, 7.4, 8.0).