feat: add packet filter management tool for GNS3-Copilot fault injection

Add comprehensive packet filter management functionality to GNS3-Copilot,
enabling AI-powered fault injection scenarios with network simulation
capabilities like latency, packet loss, and corruption.

## Changes

### New Features
- **GNS3PacketFilterTool**: New LangChain tool for managing packet filters
  on GNS3 links with support for delay, packet loss, corruption,
  frequency_drop, and BPF filtering
  - Actions: get_available, set, get, clear
  - Integrated into troubleshooting_injection mode for fault scenarios

### API Integration
- **Link.available_filters()**: Added method to custom_gns3fy.py Link class
  - Queries available filter types for specific links
  - API v3+ only (raises ValueError for v2 connectors)
  - Returns filter definitions with parameters and constraints

### Tool Integration
- Added GNS3PacketFilterTool to TROUBLESHOOTING_INJECTION_MODE_TOOLS
- Positioned as 3rd tool in fault injection workflow
- Optimized for troubleshooting practice scenarios

## Files Modified
- gns3server/agent/gns3_copilot/agent/gns3_copilot.py
- gns3server/agent/gns3_copilot/gns3_client/custom_gns3fy.py
- gns3server/agent/gns3_copilot/tools_v2/__init__.py

## Files Added
- gns3server/agent/gns3_copilot/tools_v2/gns3_packet_filter.py

## Testing
- All validation tests passed
- Version checking verified (v3+ only)
- Tool integration confirmed in troubleshooting mode

gns3server/agent/gns3_copilot/tools_v2/__init__.py

@@ -32,6 +32,7 @@ This package provides various tools for interacting with GNS3 network simulator:
 - Multiple device command execution using Nornir
 - VPCS device configuration using Netmiko
 - Node and link management
+- Packet filter management
 
 Main modules:
 - config_tools_nornir: Multiple device configuration command execution tool using Nornir
@@ -42,6 +43,7 @@ Main modules:
 - gns3_start_node: GNS3 node startup tool
 - gns3_get_node_temp: GNS3 template retrieval tool
 - gns3_update_node_name: GNS3 node name update tool
+- gns3_packet_filter: GNS3 packet filter management tool
 
 Note: GNS3TopologyTool is now available from gns3_client package
 
@@ -54,6 +56,7 @@ from .display_tools_nornir import ExecuteMultipleDeviceCommands
 from .gns3_create_link import GNS3LinkTool
 from .gns3_create_node import GNS3CreateNodeTool
 from .gns3_get_node_temp import GNS3TemplateTool
+from .gns3_packet_filter import GNS3PacketFilterTool
 from .gns3_start_node import GNS3StartNodeQuickTool
 from .gns3_start_node import GNS3StartNodeTool
 from .gns3_stop_node import GNS3StopNodeTool
@@ -79,6 +82,7 @@ __all__ = [
     "ExecuteMultipleDeviceCommands",
     "GNS3CreateNodeTool",
     "GNS3LinkTool",
+    "GNS3PacketFilterTool",
     "GNS3StartNodeTool",
     "GNS3StartNodeQuickTool",
     "GNS3StopNodeTool",