feat(neogaia): add the CachyOS kernel and hardware enablement

Select the CachyOS kernel per-Host via boot.kernelPackages, enable Intel
microcode and redistributable firmware (ath10k for the QCA6174 wifi), and
move zram behind a toggle Module. Declare the chaotic binary cache in the
base Nix settings (extra-substituters/keys) so the built system fetches the
kernel from nyx-cache rather than compiling it.

modules/zram.nix

@@ -0,0 +1,14 @@
+{ config, lib, ... }:
+# A toggle for RAM-backed swap. A Host that has no on-disk swap partition (like
+# neogaia, whose disko layout deliberately omits one) enables this to get a
+# compressed zram device instead.
+let
+  cfg = config.modules.zram;
+in
+{
+  options.modules.zram.enable = lib.mkEnableOption "zram-backed compressed swap";
+
+  config = lib.mkIf cfg.enable {
+    zramSwap.enable = true;
+  };
+}