Add 2023 R2 gRPC transport (RemoteGrpc) reusing native byte payloads

Stands up HistorianTransport.RemoteGrpc end-to-end for the read path,
built on the recovered 2023 R2 gRPC contract (gRPC-Web/HTTP-1.1, port
32565, gzip). The opaque protobuf `bytes` fields carry the SAME native
binary payloads as the 2020 WCF/MDAS path, so the proven serializers and
parsers are reused unchanged.

- Grpc/Protos/*.proto: 6 protoc-validated contracts recovered from
  embedded FileDescriptors (authoritative, not guessed).
- Grpc/HistorianGrpcChannelFactory: GrpcWebHandler/HTTP-1.1 channel,
  ResolvePort/ResolveAddress, optional TLS + gzip.
- Grpc/HistorianGrpcReadOrchestrator: mirrors the WCF read chain over
  gRPC; auth uses HistoryService.ExchangeKey (the gRPC ValCl op).
- Wcf/HistorianNativeHandshake: transport-agnostic Open2 request builder
  + SSPI/Negotiate token loop + response decode, shared by WCF and gRPC.
- Op map (2020 -> gRPC): ValCl->ExchangeKey, Open2->OpenConnection,
  StartQuery2->StartQuery, GetNextQueryResultBuffer2->GetNextQueryResultBuffer.
- HistorianClientOptions: DefaultGrpcPort=32565, GrpcUseTls.
- csproj: Google.Protobuf, Grpc.Net.Client(.Web), Grpc.Tools codegen.

Not yet live-verified against a 2023 R2 server: ExchangeKey is the first
thing to revisit if a live server rejects the handshake; the inner byte
payloads are the proven 2020 protocol. Gated live test via
HISTORIAN_GRPC_HOST. 188 unit tests green; build clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AVEVA.Historian.Client/Protocol/Historian2020ProtocolDialect.cs

@@ -1,3 +1,4 @@
+using AVEVA.Historian.Client.Grpc;
 using AVEVA.Historian.Client.Models;
 using AVEVA.Historian.Client.Wcf;
 
@@ -12,23 +13,28 @@ internal sealed class Historian2020ProtocolDialect
         _options = options ?? throw new ArgumentNullException(nameof(options));
     }
 
+    private bool UseGrpc => _options.Transport == HistorianTransport.RemoteGrpc;
+
     public IAsyncEnumerable<HistorianSample> ReadRawAsync(string tag, DateTime startUtc, DateTime endUtc, int maxValues, CancellationToken cancellationToken)
     {
-        HistorianWcfReadOrchestrator orchestrator = new(_options);
-        return orchestrator.ReadRawAsync(tag, startUtc, endUtc, maxValues, cancellationToken);
+        return UseGrpc
+            ? new HistorianGrpcReadOrchestrator(_options).ReadRawAsync(tag, startUtc, endUtc, maxValues, cancellationToken)
+            : new HistorianWcfReadOrchestrator(_options).ReadRawAsync(tag, startUtc, endUtc, maxValues, cancellationToken);
     }
 
     public IAsyncEnumerable<HistorianAggregateSample> ReadAggregateAsync(string tag, DateTime startUtc, DateTime endUtc, RetrievalMode mode, TimeSpan interval, CancellationToken cancellationToken)
     {
-        HistorianWcfReadOrchestrator orchestrator = new(_options);
-        return orchestrator.ReadAggregateAsync(tag, startUtc, endUtc, mode, interval, cancellationToken);
+        return UseGrpc
+            ? new HistorianGrpcReadOrchestrator(_options).ReadAggregateAsync(tag, startUtc, endUtc, mode, interval, cancellationToken)
+            : new HistorianWcfReadOrchestrator(_options).ReadAggregateAsync(tag, startUtc, endUtc, mode, interval, cancellationToken);
     }
 
     public Task<IReadOnlyList<HistorianSample>> ReadAtTimeAsync(string tag, IReadOnlyList<DateTime> timestampsUtc, CancellationToken cancellationToken)
     {
         cancellationToken.ThrowIfCancellationRequested();
-        HistorianWcfReadOrchestrator orchestrator = new(_options);
-        return orchestrator.ReadAtTimeAsync(tag, timestampsUtc, cancellationToken);
+        return UseGrpc
+            ? new HistorianGrpcReadOrchestrator(_options).ReadAtTimeAsync(tag, timestampsUtc, cancellationToken)
+            : new HistorianWcfReadOrchestrator(_options).ReadAtTimeAsync(tag, timestampsUtc, cancellationToken);
     }
 
     public IAsyncEnumerable<HistorianBlock> ReadBlocksAsync(string tag, DateTime startUtc, DateTime endUtc, CancellationToken cancellationToken)