nezha: 0.20.3 -> 1.6.3; nezha-agent: 0.20.5 -> 1.6.0; nixos/nezha-agent: refactor

nezha: 0.20.3 -> 1.6.3; nezha-agent: 0.20.5 -> 1.6.0; nixos/nezha-agent: refactor #3698