proxy, ui: add pending requests count to the main dashboard (#516)

add a real time counter of pending (inflight) requests to the UI.

proxy/events.go

@@ -8,6 +8,7 @@ const ConfigFileChangedEventID = 0x03
 const LogDataEventID = 0x04
 const TokenMetricsEventID = 0x05
 const ModelPreloadedEventID = 0x06
+const InFlightRequestsEventID = 0x07
 
 type ProcessStateChangeEvent struct {
 	ProcessName string
@@ -58,3 +59,11 @@ type ModelPreloadedEvent struct {
 func (e ModelPreloadedEvent) Type() uint32 {
 	return ModelPreloadedEventID
 }
+
+type InFlightRequestsEvent struct {
+	Total int
+}
+
+func (e InFlightRequestsEvent) Type() uint32 {
+	return InFlightRequestsEventID
+}