fix(telemetry): fully qualify RPC method attribute

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: ReubenBond

src/Orleans.Core/Diagnostics/ActivityPropagationGrainCallFilter.cs

@@ -52,7 +52,7 @@ protected static async Task Process(IGrainCallContext context, Activity activity
                 // RPC attributes from https://opentelemetry.io/docs/specs/semconv/rpc/
                 activity.SetTag(ActivityTagKeys.RpcSystem, RpcSystem);
                 activity.SetTag(ActivityTagKeys.RpcService, context.InterfaceName);
-                activity.SetTag(ActivityTagKeys.RpcMethod, context.MethodName);
+                activity.SetTag(ActivityTagKeys.RpcMethod, $"{context.InterfaceName}/{context.MethodName}");
 
                 if (activity.IsAllDataRequested)
                 {

test/Orleans.Runtime.Tests/GrainCallTraceContextPropagationTests.cs

@@ -115,7 +115,9 @@ public async Task GrainCallUsesCurrentRpcSemanticConventionKeys()
             Assert.NotNull(activity);
             Assert.Equal("orleans", activity.GetTagItem("rpc.system.name"));
             Assert.Equal(typeof(ITraceContextPropagationGrain).FullName, activity.GetTagItem("orleans.rpc.service"));
-            Assert.Equal(nameof(ITraceContextPropagationGrain.GetTraceContextInfo), activity.GetTagItem("rpc.method"));
+            Assert.Equal(
+                $"{typeof(ITraceContextPropagationGrain).FullName}/{nameof(ITraceContextPropagationGrain.GetTraceContextInfo)}",
+                activity.GetTagItem("rpc.method"));
             Assert.Null(activity.GetTagItem("rpc.system"));
             Assert.Null(activity.GetTagItem("rpc.service"));
             Assert.NotNull(activity.GetTagItem("orleans.rpc.target_id"));