nixos/git-worktree-switcher: init git-worktree-switcher

This module sets up shells so that they work with
[git-worktree-switcher](https://github.com/mateusauler/git-worktree-switcher)

nixos/doc/manual/release-notes/rl-2505.section.md

···
 
 - [agorakit](https://github.com/agorakit/agorakit), an organization tool for citizens' collectives. Available with [services.agorakit](#opt-services.agorakit.enable).
 
+- [git-worktree-switcher](https://github.com/mateusauler/git-worktree-switcher), switch between git worktrees with speed. Available as [programs.git-worktree-switcher](#opt-programs.git-worktree-switcher.enable)
+
 <!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->
 
 ## Backward Incompatibilities {#sec-release-25.05-incompatibilities}

nixos/modules/module-list.nix

···
   ./programs/gdk-pixbuf.nix
   ./programs/geary.nix
   ./programs/git.nix
+  ./programs/git-worktree-switcher.nix
   ./programs/gnome-disks.nix
   ./programs/gnome-terminal.nix
   ./programs/gnupg.nix

nixos/modules/programs/git-worktree-switcher.nix

···
+{
+  config,
+  pkgs,
+  lib,
+  ...
+}:
+
+let
+  cfg = config.programs.git-worktree-switcher;
+
+  initScript =
+    shell:
+    if (shell == "fish") then
+      ''
+        ${lib.getExe pkgs.git-worktree-switcher} init ${shell} | source
+      ''
+    else
+      ''
+        eval "$(${lib.getExe pkgs.git-worktree-switcher} init ${shell})"
+      '';
+in
+{
+  options = {
+    programs.git-worktree-switcher = {
+      enable = lib.mkEnableOption "git-worktree-switcher, switch between git worktrees with speed.";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    environment.systemPackages = with pkgs; [ git-worktree-switcher ];
+
+    programs.bash.interactiveShellInit = initScript "bash";
+    programs.zsh.interactiveShellInit = lib.optionalString config.programs.zsh.enable (
+      initScript "zsh"
+    );
+    programs.fish.interactiveShellInit = lib.optionalString config.programs.fish.enable (
+      initScript "fish"
+    );
+  };
+}