feat(config, usage): add usage-statistics-enabled option and dynamic toggling

- Introduced `usage-statistics-enabled` configuration to control in-memory usage aggregation.
- Updated API to include handlers for managing `usage-statistics-enabled` and `logging-to-file` options.
- Enhanced `watcher` to log changes to both configurations dynamically.
- Updated documentation and examples to reflect new configuration options.

internal/usage/logger_plugin.go

@@ -7,13 +7,17 @@ import (
 	"context"
 	"fmt"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/gin-gonic/gin"
 	coreusage "github.com/router-for-me/CLIProxyAPI/v6/sdk/cliproxy/usage"
 )
 
+var statisticsEnabled atomic.Bool
+
 func init() {
+	statisticsEnabled.Store(true)
 	coreusage.RegisterPlugin(NewLoggerPlugin())
 }
 
@@ -36,12 +40,21 @@ func NewLoggerPlugin() *LoggerPlugin { return &LoggerPlugin{stats: defaultReques
 //   - ctx: The context for the usage record
 //   - record: The usage record to aggregate
 func (p *LoggerPlugin) HandleUsage(ctx context.Context, record coreusage.Record) {
+	if !statisticsEnabled.Load() {
+		return
+	}
 	if p == nil || p.stats == nil {
 		return
 	}
 	p.stats.Record(ctx, record)
 }
 
+// SetStatisticsEnabled toggles whether in-memory statistics are recorded.
+func SetStatisticsEnabled(enabled bool) { statisticsEnabled.Store(enabled) }
+
+// StatisticsEnabled reports the current recording state.
+func StatisticsEnabled() bool { return statisticsEnabled.Load() }
+
 // RequestStatistics maintains aggregated request metrics in memory.
 type RequestStatistics struct {
 	mu sync.RWMutex
@@ -138,6 +151,9 @@ func (s *RequestStatistics) Record(ctx context.Context, record coreusage.Record)
 	if s == nil {
 		return
 	}
+	if !statisticsEnabled.Load() {
+		return
+	}
 	timestamp := record.RequestedAt
 	if timestamp.IsZero() {
 		timestamp = time.Now()