Replace NodeStats forward_scheduling_delay with processing per subscriber (#1895)

* Replace NodeStats forward_scheduling_delay with forward_processing_per_subscriber

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* generated protobuf

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: github-actions <41898282+github-actions[bot]@users.noreply.github.com>

Author: 3 people

.changeset/forward-processing-per-subscriber.md

@@ -0,0 +1,6 @@
+---
+"github.com/livekit/protocol": patch
+"@livekit/protocol": patch
+---
+
+Replace `NodeStats.forward_scheduling_delay` with `NodeStats.forward_processing_per_subscriber`, the mean forwarding work per subscriber written

livekit/livekit_internal.pb.go

@@ -126,8 +126,8 @@ message NodeStats {
   // forward metrics
   uint32 forward_latency = 48;
   uint32 forward_jitter = 49 [deprecated = true];
-  // p90 time from arrival to dequeue, in ns, for packets that found their forwarder idle
-  uint32 forward_scheduling_delay = 57;
+  // mean forwarding work per subscriber, in ns: (end of fan-out - dequeue) / subscribers written
+  uint32 forward_processing_per_subscriber = 57;
 
   repeated NodeStatsRate rates = 50;