Include metrics from upstream chat requests (#361)

* proxy: refactor metrics recording

- remove metrics_middleware.go as this wrapper is no longer needed. This
  also eliminiates double body parsing for the modelID
- move metrics parsing to be part of MetricsMonitor
- refactor how metrics are recording in ProxyManager
- add MetricsMonitor tests
- improve mem efficiency of processStreamingResponse
- add benchmarks for MetricsMonitor.addMetrics
- proxy: refactor MetricsMonitor to be more safe handling errors

proxy/proxymanager_api.go

@@ -180,7 +180,7 @@ func (pm *ProxyManager) apiSendEvents(c *gin.Context) {
 	sendLogData("proxy", pm.proxyLogger.GetHistory())
 	sendLogData("upstream", pm.upstreamLogger.GetHistory())
 	sendModels()
-	sendMetrics(pm.metricsMonitor.GetMetrics())
+	sendMetrics(pm.metricsMonitor.getMetrics())
 
 	for {
 		select {
@@ -198,7 +198,7 @@ func (pm *ProxyManager) apiSendEvents(c *gin.Context) {
 }
 
 func (pm *ProxyManager) apiGetMetrics(c *gin.Context) {
-	jsonData, err := pm.metricsMonitor.GetMetricsJSON()
+	jsonData, err := pm.metricsMonitor.getMetricsJSON()
 	if err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to get metrics"})
 		return