fix(symfony): throw on route name collisions between resource classes

[audain-dg]

Q	A
Branch?	main
Tickets	n/a
License	MIT
Doc PR	n/a

What

Operation names double as Symfony route names, and ApiLoader registers them with RouteCollection::add(), which silently replaces an existing entry. Two resource classes exposing the same URI template and method therefore end up with one route only, owned by whichever class was discovered last, with no error or warning. The winner can flip on cache:clear when the discovery order changes.

MetadataCollectionFactoryTrait::assertOperationNameIsUnique() (4.3) already rejects a duplicate name within one class. This PR extends the guarantee across classes:

• two exposed operations from different classes under one name now throw a RuntimeException naming both classes, and pointing to routeName as the supported way to share a route on purpose;
• a NotExposed placeholder never wins over an exposed operation of another class, whatever the discovery order, and never throws (a DTO and an entity sharing a shortName keep working).

Why it matters

The test application itself had four such collisions, each silently dropping a route:

Operation name	Loser	Winner
_api_/user-actions_get_collection	Issue7916\UserActionResource (ORM)	UserActionResourceOdm
_api_/companies/{companyId}/employees/{id}_get	DummyResourceWithComplexConstructor	Employee
_api_/books/{id}{._format}_get	IriFilterRelationsTest\Book (NotExposed)	Entity\Book
_api_/people/{id}{._format}_get	Issue5438\Person (NotExposed)	Entity\Person

Nobody noticed because functional tests restrict resources per test class. In a real application the same thing happens when two resources (an ORM/ODM pair, a DTO and its entity, two projections of one entity) share a URI template.

The first two fixtures now use distinct URI templates; the last two are covered by the placeholder rule.

Notes

• Targets main because a silent overwrite becomes an exception. Happy to retarget 4.3 if you consider it a plain bug fix.
• ApiLoaderTest::testApiLoader was asserting RelatedDummyEntity::class on every route, i.e. it was asserting the overwrite: both classes returned the same metadata collection. The helper now gives the second class an empty collection by default.
• Sharing a route on purpose is unchanged: a resource declaring routeName creates no route (ApiLoader skips it) and is not affected. Covered by a new test.