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>

config.yml.example

@@ -4,27 +4,33 @@
 core:
   # Network interface to capture traffic from
   interface: eth0
-  
+
   # TCP ports to monitor for TLS handshakes
   listen_ports:
     - 443
     - 8443
-  
+
   # Optional BPF filter (leave empty for auto-generated filter based on listen_ports)
   bpf_filter: ""
 
+  # Timeout in seconds for TLS handshake extraction (default: 30)
+  flow_timeout_sec: 30
+
+  # Buffer size for packet channel (default: 1000, increase for high-traffic environments)
+  packet_buffer_size: 1000
+
 outputs:
   # Output to stdout (JSON lines)
   - type: stdout
     enabled: true
     params: {}
-  
+
   # Output to file
   # - type: file
   #   enabled: false
   #   params:
   #     path: /var/log/ja4sentinel/ja4.log
-  
+
   # Output to UNIX socket (for systemd/journald or other consumers)
   # - type: unix_socket
   #   enabled: false