Inline request/reply over the Wolverine.Grpc transport (GH-2967)

[jeremydmiller]

Closes #2967. Companion to #2966/#2990 (HTTP inline request/reply), built on the shared IInlineRequestReplyEndpoint / MessageRoute.For infrastructure that merged with #2990.

What

InvokeAsync<T> routed to a gRPC endpoint now reads the reply straight off a new unary Call(WolverineMessage) returns (WolverineMessage) RPC — no ReplyListener, no listening endpoint on the sender, no TaskCompletionSource reply choreography. gRPC's unary response slot carries the reply envelope in the same exchange.

How

• wolverine.proto — new rpc Call(WolverineMessage) returns (WolverineMessage); request carries the serialized request envelope, response carries the serialized reply (which may be a FailureAcknowledgement).
• GrpcEndpoint now implements IInlineRequestReplyEndpoint, so MessageRoute.For(...) selects the InlineReplyMessageRoute subclass — no runtime if/then (the same shape Jeremy asked for in Optimized inline request/reply over the Wolverine.Http transport (GH-2966) #2990). InvokeRemoteAsync serializes the request, calls the unary RPC over a cached GrpcChannel/client, and deserializes the reply. An RpcException (transport-level failure) maps to a FailureAcknowledgement reply so the caller still gets the usual WolverineRequestReplyException.
• Receiver Call handler mirrors the HTTP transport executor: deserialize the request, set ResponseType from ReplyRequested, run executor.InvokeInlineAsync (flushing the outbox before the response), and return Envelope.Response. Handler failures / missing handlers come back as a FailureAcknowledgement reply. MessageTracking.MessageSucceeded fires on every success path so tracked sessions quiesce.

Tests

• New inline_request_reply_grpc — happy path asserts the reply is read off the gRPC response slot (sender has no reply listener, so a pass proves the inline path); failure path asserts a handler throw surfaces as WolverineRequestReplyException.
• GrpcTransportCompliance.can_request_reply passes unchanged against the inline path.
• Full gRPC suite: 218/218 green. dotnet build wolverine.slnx -c Release clean.

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