Make index dispatches failure-safe (and confirm async marker interface)

[loevgaard]

What

Out of the box every save of an indexable entity dispatches on the plugin's command bus, and since no transport routing is configured, the handler runs synchronously inside the Doctrine flush. If Meilisearch was slow or down, saving/deleting a product failed — a search-index hiccup broke catalog management.

Two parts:

1. Resilience for the sync default. EntityListener now wraps every dispatch in try/catch and logs the failure at error (dedicated setono_sylius_meilisearch Monolog channel). A failed index update — or a transport outage on an async setup — can never break the entity save it reacts to.
2. First-class async support. All plugin command messages already share the CommandInterface marker (directly or via EntityAwareCommand), so a single framework.messenger.routing entry can route everything to an async transport. The recommended routing snippet is documented in the operational-model docs issue ([Docs]: Document the operational model - async indexing, settings sync, production checklist #140).

Testing

EntityListenerTest::it_swallows_and_logs_a_failing_dispatch_so_the_entity_save_still_succeeds: with the command bus throwing, postPersist does not throw and an error is logged.

Closes #124

---

Stacked on #157 (#112).

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (issue-112-incremental-default-filters@be49d96). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/EventListener/Doctrine/EntityListener.php	87.50%	1 Missing ⚠️

Additional details and impacted files

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##             issue-112-incremental-default-filters     #158   +/-   ##
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