nixos/kmonad: create determinate symlinks (#370053)

- For matrix homeserver Synapse we are now following the upstream recommendation to enable jemalloc as the memory allocator by default.

- `services.kmonad` now creates a determinate symlink (in `/dev/input/by-id/`) to each of KMonad virtual devices.

- `bind.cacheNetworks` now only controls access for recursive queries, where it previously controlled access for all queries.

- Caddy can now be built with plugins by using `caddy.withPlugins`, a `passthru` function that accepts an attribute set as a parameter. The `plugins` argument represents a list of Caddy plugins, with each Caddy plugin being a versioned module. The `hash` argument represents the `vendorHash` of the resulting Caddy source code with the plugins added.

  config = lib.mkIf cfg.enable {

    hardware.uinput.enable = true;

    services.udev.extraRules =

      let

        mkRule = name: ''

          ACTION=="add", KERNEL=="event*", SUBSYSTEM=="input", ATTRS{name}=="${name}", ATTRS{id/product}=="5679", ATTRS{id/vendor}=="1235", SYMLINK+="input/by-id/${name}"

        '';

      in

      lib.foldlAttrs (

        rules: _: keyboard:

        rules + "\n" + mkRule (mkName keyboard.name)

      ) "" cfg.keyboards;

    systemd = {

      paths = lib.mapAttrs' (_: mkPath) cfg.keyboards;

      services = lib.mapAttrs' (_: mkService) cfg.keyboards;

    with subtest("kmonad is running"):

         machine.succeed(f"systemctl status {service_name}")

    with subtest("kmonad symlink is created"):

         machine.wait_for_file(f"/dev/input/by-id/{service_name}", timeout=5)

  '';

}