feat: define StreamStore/ConsumerStore interfaces from Go store.go

Port IStreamStore, IConsumerStore, StoreMsg, StreamState, SimpleState,
ConsumerState, FileStoreConfig, StoreCipher, StoreCompression types.
Rename Models.StreamState → ApiStreamState to avoid namespace conflict.

tests/NATS.Server.Tests/JetStreamApiFixture.cs

@@ -206,7 +206,7 @@ internal sealed class JetStreamApiFixture : IAsyncDisposable
         return RequestLocalAsync($"$JS.API.STREAM.CREATE.{streamName}", payload);
     }
 
-    public Task<StreamState> GetStreamStateAsync(string streamName)
+    public Task<ApiStreamState> GetStreamStateAsync(string streamName)
     {
         return _streamManager.GetStateAsync(streamName, default).AsTask();
     }