Add linting, formatting, and CI with fixes for all warnings

Infrastructure:
- Add deadnix, nixfmt, and statix to flake inputs
- Add formatter output to flake for nix fmt support
- Add deadnix, nixfmt, statix to Home Manager packages
- Add GitHub Actions workflow for CI validation
- Add .pre-commit-config.yaml with hooks for nixfmt, deadnix, and statix
- Support x86_64-darwin in formatter

Statix fixes (W10/W20 warnings):
- Remove unused lambda argument from nixpkgs-settings.nix
- Merge repeated keys in hardware-configuration.nix files (boot.initrd, boot, fileSystems)
- Merge repeated keys in nixnuc/default.nix (services, virtualisation)
- Merge repeated keys in rainbow-planet/default.nix (desktopManager)
- Merge repeated keys in home/general/default.nix (home)

Deadnix fixes (unused declarations):
- Remove unused pkgs/lib/username/http_port arguments from various files
- Fix unused final parameter in overlay functions (final -> _final)

CI/pre-commit fixes:
- Fix pre-commit statix config: add pass_filenames: false
- Fix CI workflow: use nix run nixpkgs# prefix and --ci flag for nixfmt

modules/hosts/nixos/nixnuc/containers/audiobookshelf.nix

@@ -1,7 +1,9 @@
-{ ... }: let
+_:
+let
   volume_base = "/var/lib/audiobookshelf";
   http_port = "13378";
-in {
+in
+{
   # Audiobookshelf
 
   virtualisation.oci-containers.containers = {

modules/hosts/nixos/nixnuc/containers/mountain-mesh-bot-discord.nix

@@ -1,6 +1,8 @@
-{ config, username, ... }: let
+{ config, ... }:
+let
   volume_base = "/orico/mountain-mesh-bot-discord";
-in {
+in
+{
   # My mountain-mesh-bot-discord container
 
   virtualisation.oci-containers.containers = {
@@ -17,6 +19,8 @@ in {
 
   sops.secrets.mtnmesh_bot_dot_env = {
     path = "${volume_base}/.env";
-    restartUnits = [ "${config.virtualisation.oci-containers.containers.mtnmesh_bot_discord.serviceName}" ];
+    restartUnits = [
+      "${config.virtualisation.oci-containers.containers.mtnmesh_bot_discord.serviceName}"
+    ];
   };
 }

modules/hosts/nixos/nixnuc/containers/psitransfer.nix

@@ -1,8 +1,10 @@
-{ config, ... }: let
+{ config, ... }:
+let
   volume_base = "/orico/psitransfer";
   http_port = "3000";
   psitransfer_dot_env = "${config.sops.secrets.psitransfer_dot_env.path}";
-in {
+in
+{
 
   #############################################################################
   # My intent as of now is to only make this available to the outside world   #
@@ -29,4 +31,3 @@ in {
     };
   };
 }
-