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/HistorianClientOptions.cs

@@ -6,6 +6,9 @@ public sealed class HistorianClientOptions
 {
     public const int DefaultPort = 32568;
 
+    /// <summary>Default TCP port of the 2023 R2 Historian Client Access Point gRPC endpoint.</summary>
+    public const int DefaultGrpcPort = 32565;
+
     public required string Host { get; init; }
 
     public int Port { get; init; } = DefaultPort;
@@ -49,4 +52,14 @@ public sealed class HistorianClientOptions
     /// that don't validate a server certificate.
     /// </summary>
     public string? ServerDnsIdentity { get; init; }
+
+    /// <summary>
+    /// For <see cref="HistorianTransport.RemoteGrpc"/>: when true the channel uses TLS
+    /// (<c>https://</c>); when false it uses plaintext (<c>http://</c>). Matches the stock
+    /// 2023 R2 client's <c>securedConnection</c> flag. The TLS host is taken from
+    /// <see cref="ServerDnsIdentity"/> when set (to match the server certificate's name),
+    /// otherwise <see cref="Host"/>. When <see cref="AllowUntrustedServerCertificate"/> is
+    /// true the server certificate chain is not validated. Default false.
+    /// </summary>
+    public bool GrpcUseTls { get; init; }
 }