feat(usage): implement usage tracking infrastructure across executors

- Added `LoggerPlugin` to log usage metrics for observability.
- Introduced a new `Manager` to handle usage record queuing and plugin registration.
- Integrated new usage reporter and detailed metrics parsing into executors, covering providers like OpenAI, Codex, Claude, and Gemini.
- Improved token usage breakdown across streaming and non-streaming responses.

internal/usage/logger_plugin.go

@@ -0,0 +1,26 @@
+package usage
+
+import (
+	"context"
+	"encoding/json"
+
+	coreusage "github.com/router-for-me/CLIProxyAPI/v6/sdk/cliproxy/usage"
+	log "github.com/sirupsen/logrus"
+)
+
+func init() {
+	coreusage.RegisterPlugin(NewLoggerPlugin())
+}
+
+// LoggerPlugin outputs every usage record to the application log.
+type LoggerPlugin struct{}
+
+// NewLoggerPlugin constructs a new logger plugin instance.
+func NewLoggerPlugin() *LoggerPlugin { return &LoggerPlugin{} }
+
+// HandleUsage implements coreusage.Plugin.
+func (p *LoggerPlugin) HandleUsage(ctx context.Context, record coreusage.Record) {
+	// Output all relevant fields for observability; keep logging lightweight and non-blocking.
+	data, _ := json.Marshal(record)
+	log.Debug(string(data))
+}