Flow ExecutionContext with JsonRpcMessage (#616)

The primary goal of this change is to support IHttpContextAccessor in tool calls when the Streamable HTTP is in its default non-Stateless mode.

src/ModelContextProtocol.AspNetCore/StreamableHttpHandler.cs

@@ -188,6 +188,7 @@ internal sealed class StreamableHttpHandler(
             transport = new()
             {
                 SessionId = sessionId,
+                FlowExecutionContextFromRequests = !HttpServerTransportOptions.PerSessionExecutionContext,
             };
             context.Response.Headers[McpSessionIdHeaderName] = sessionId;
         }