[jeremydmiller]

Closes #1102.

SubscriptionDescriptor only said what a projection produces through AggregateType, which is null for event projections and composites. A tool reading the descriptor couldn't link those projections to the documents they write, even though PublishedTypes() already knew.

What changes

• SubscriptionDescriptor.PublishedTypes is a new TypeDescriptor[]: distinct, in ordinal order by full name, and never null. AggregateType is untouched.
• IPublishesTypes is a new non-generic interface, so the descriptor constructor needs no generics. Every IProjectionSource<,> gets it through a default body, and PublishedTypes() stays declared on IProjectionSource<,> with new, so stores compiled against it and explicit implementers keep working.
• A real bug in the scoped wrapper. ProjectionSourceWrapperBase hid its types behind an explicit interface implementation beside ProjectionBase's public method, and its Describe() reports a freshly resolved instance that never saw the registration's Options. It now overrides the method and supplies the list itself.
• InMemoryDocumentStore.TryCreateUsage now calls Projections.Describe. Without it the store reported no projections at all and couldn't pass the new compliance check.
• Compliance: six new facts in EventProjectionRegistrationCompliance.

Decisions worth checking

• Empty does not mean "writes nothing". A subscription writes nothing, but a flat table projection writes rows with no type, and a bare IProjection never says. The docs say so.
• Describing can't fail because of this field. A PublishedTypes() that throws or returns null gives an empty list rather than losing the whole Describe() pipeline, the same call the descriptor makes for ImplementationType. That case looks the same as an empty answer.
• void, Task and ValueTask are filtered out. An event projection records Create return types in its constructor, ahead of validation, so they can appear on a projection nothing has validated yet.

The issue's open question: EF Core projections

• Single and multi stream EF Core projections return TDoc, the entity type, in Marten and Polecat. Fisher has no such classes, but an ordinary projection routed with ProjectToEfCore also returns TDoc.
• EfCoreEventProjection returns nothing in all three stores unless something declares a type. Marten's isn't a ProjectionBase, so only a registration-time teardown rule can add one.

So a consumer can resolve single and multi stream projections against DbContext entity lists, but not EF event projections. Other entities a projection touches through its DbContext are never listed.

Release note

• New SubscriptionDescriptor.PublishedTypes and IPublishesTypes. IProjectionSource<,> now inherits IPublishesTypes.
• On scoped source wrappers, PublishedTypes() called through a ProjectionBase reference now returns the full set. It used to return only Options.StorageTypes.
• TryCreateUsage on the in-memory store now lists its projections.

Additive on the wire: an old payload or a null field reads as empty, and an older reader ignores the field. Both are tested.

Testing

Full gate on this branch, locally on net9.0 and net10.0: 7,808 passed, 0 failed, 66 skipped. It ran before #1103 merged; this branch merges cleanly with main, but the combination hasn't been run. Each guard was mutation-tested, and all 8 mutants were killed. One survived at first because assembly copied types into Options.StorageTypes, so its test was made stronger.

The compliance suite ships as source, so it was validated against real stores from a local pack (2.97.1-local.1102):

Store	Backend	event_projection_registration_compliance, net10.0 and net9.0
Fisher	SQLite	9 of 9 on each
Polecat	SQL Server	9 of 9 on each
Marten	Postgres 15.3	9 of 9 on each

• Removing Describe from each store made exactly the 6 new facts fail, so the passes aren't vacuous.
• Fisher's whole compliance folder on net10.0: 757 passed, 0 failed, 22 skipped.
• Binary compatibility: an assembly built against released 2.97.0 loaded and described itself beside this branch for three source shapes, and throws TypeLoadException if the default body is removed.

No store needs a change.

Not covered

• A store's CompositeIProjectionSource and its scoped registrations can't be reached by a store-neutral suite. Those were checked by reading only.
• Marten ran on Postgres 15.3, not its compose image (Postgres 17 with NAMEDATALEN 100). Polecat's and Marten's wider suites weren't run, only this class.
• CritterWatch and Wolverine, as readers of the descriptor, weren't checked.
• The in-memory store's usage.Events and RegisteredEventTypes stay empty, and it stays unenrolled from the explorer suite.

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