feat(copilot): add VPCS Telnet driver with Netmiko and ANSI code stripping

Implement custom VPCS driver and unified tool architecture:

   - Add VPCSTelnet custom driver (vpcs_telnet.py)
     - No authentication (direct console access like VPCS behavior)
     - Simple prompt pattern matching (PC\d+>)
     - Automatic ANSI escape code stripping for clean output
     - Config mode methods return empty (VPCS has no config modes)

   - Replace vpcs_tools_telnetlib3.py with vpcs_tools_netmiko.py
     - Migrate from telnetlib3 to Netmiko + Nornir architecture
     - Unified tool architecture matching config/display tools
     - Improved code consistency and maintainability

   - Add comprehensive test coverage (test_vpcs_telnet.py)
     - 30 unit tests covering all VPCS driver functionality
     - Tests for ANSI code stripping, telnet_login, send_command
     - Tests for device registration and initialization

   - Update VPCS built-in template (services/templates.py)
     - Add platform:vpcs and device_type:gns3_vpcs_telnet tags
     - Automatic driver selection without manual configuration

   - Update documentation (docs/)
     - multi-vendor-device-support.md: VPCS driver documentation
     - netmiko_devices.md: Add VPCS to supported devices list
     - README.md: Update multi-vendor support description

gns3server/services/templates.py

@@ -110,6 +110,7 @@ BUILTIN_TEMPLATES = [
         "base_script_file": "vpcs_base_config.txt",
         "compute_id": None,
         "builtin": True,
+        "tags": ["platform:vpcs", "device_type:gns3_vpcs_telnet"],
     },
     {
         "template_id": uuid.uuid5(uuid.NAMESPACE_X500, "ethernet_switch"),