Release v22.150.0

Added

• The Arc source generator registers the element type of every model-bound observable query that returns ISubject<T> or IAsyncEnumerable<T>, so WebSocket, Server-Sent Events and HTTP handling use statically typed operations instead of closing generic methods at runtime. Under the JIT, unregistered element types keep the cached reflection path; in ahead-of-time compiled code they fail with MissingObservableQueryElementType, naming the type. (part of #2855)