proxy: Improve logging performance and allow separate log streaming (#421)

Replace container/ring.Ring with a custom circularBuffer that uses a
single contiguous []byte slice. This fixes the original implementation
which created 10,240 ring elements instead of 10KB of storage.

GetHistory is now 139x faster (145μs → 1μs) and uses 117x less memory
(1.2MB → 10KB). Allocations reduced from 2 to 1 per write operation.

Create a LogMonitor per proxy.Process, replacing the usage
of a shared one. The buffer in LogMonitor is lazy allocated on the first
call to Write and freed when the Process is stopped. This reduces
unnecessary memory usage when a model is not active.

The /logs/stream/{model_id} endpoint was added to stream logs from a
specific process.

proxy/proxymanager_loghandlers.go

@@ -83,18 +83,24 @@ func (pm *ProxyManager) streamLogsHandler(c *gin.Context) {
 
 // getLogger searches for the appropriate logger based on the logMonitorId
 func (pm *ProxyManager) getLogger(logMonitorId string) (*LogMonitor, error) {
-	var logger *LogMonitor
-
-	if logMonitorId == "" {
+	switch logMonitorId {
+	case "":
 		// maintain the default
-		logger = pm.muxLogger
-	} else if logMonitorId == "proxy" {
-		logger = pm.proxyLogger
-	} else if logMonitorId == "upstream" {
-		logger = pm.upstreamLogger
-	} else {
+		return pm.muxLogger, nil
+	case "proxy":
+		return pm.proxyLogger, nil
+	case "upstream":
+		return pm.upstreamLogger, nil
+	default:
+		// search for a models specific logger
+		if name, found := pm.config.RealModelName(logMonitorId); found {
+			for _, group := range pm.processGroups {
+				if process, found := group.GetMember(name); found {
+					return process.Logger(), nil
+				}
+			}
+		}
+
 		return nil, fmt.Errorf("invalid logger. Use 'proxy' or 'upstream'")
 	}
-
-	return logger, nil
 }