`google/protobuf/go_features.proto : error : File not found` when generating C# code

I have a .proto file starting with:

```proto
edition = "2023";

import "google/protobuf/go_features.proto";
option features.(pb.go).api_level = API_OPAQUE;

option go_package = "...";
option csharp_namespace = "...";

import "google/protobuf/struct.proto";
import "google/protobuf/timestamp.proto";

message Message {
...
}
```

When trying to generate C# gRPC code for this proto file I get an error message:

```
google/protobuf/go_features.proto : error : File not found. [/.../....csproj]
proto/proto.proto(3,1): error : Import "google/protobuf/go_features.proto" was not found or had errors. [/.../....csproj]
```

Compiling protobuf files that don't import go_features.proto seems to work fine.

Start with proto/proto.proto and the .csproj configuration, then inspect how the C# gRPC generator resolves imported Google protobuf files. Compare the failing google/protobuf/go_features.proto import with the working struct.proto and timestamp.proto imports; done means C# generation succeeds for the shown proto without the file-not-found errors.

Written by the indexing model from the issue text.