Add NSIS_HOOK_PREINSTALL macro that stops WireGuardTunnel$NexaVPN service, kills nexavpn-desktop.exe and nexavpn-tunnel-helper.exe processes, and stops NexaVPNTunnelService before installation. Add WireGuardTunnel$NexaVPN service stop to NSIS_HOOK_PREUNINSTALL before service uninstallation.