feat(config): add configurable packet channel buffer size

- Add PacketBufferSize field to api.Config struct
- Add DefaultPacketBuffer constant (1000 packets)
- Add JA4SENTINEL_PACKET_BUFFER_SIZE environment variable support
- Update mergeConfigs to handle PacketBufferSize override
- Update main.go to use configurable buffer size with fallback
- Update config.yml.example with packet_buffer_size option

Allows tuning for high-traffic environments by increasing buffer size
via config file or environment variable

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

internal/config/loader.go

@@ -97,6 +97,13 @@ func (l *LoaderImpl) loadFromEnv(config api.AppConfig) api.AppConfig {
 		}
 	}
 
+	// JA4SENTINEL_PACKET_BUFFER_SIZE
+	if val := os.Getenv("JA4SENTINEL_PACKET_BUFFER_SIZE"); val != "" {
+		if size, err := strconv.Atoi(val); err == nil && size > 0 {
+			config.Core.PacketBufferSize = size
+		}
+	}
+
 	return config
 }
 
@@ -144,6 +151,10 @@ func mergeConfigs(base, override api.AppConfig) api.AppConfig {
 		result.Core.FlowTimeoutSec = override.Core.FlowTimeoutSec
 	}
 
+	if override.Core.PacketBufferSize > 0 {
+		result.Core.PacketBufferSize = override.Core.PacketBufferSize
+	}
+
 	if len(override.Outputs) > 0 {
 		result.Outputs = override.Outputs
 	}