nixos/hypridle: make hypridle start with graphical-session.target

[JohnRTitor]

If we don't add the dependency explicitly, the service won't be pulled in at runtime. Link: #340874 (comment)

Closes: #347651

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[JohnRTitor]

Tested with my configuration.

❯  systemctl --user status hypridle.service
● hypridle.service - Hyprland's idle daemon
     Loaded: loaded (/etc/systemd/user/hypridle.service; enabled; preset: ignored)
    Drop-In: /nix/store/vbz308lam4ny1j73hnbvsjmzp1z3flyv-user-units/hypridle.service.d
             └─overrides.conf
     Active: active (running) since Thu 2024-10-10 10:30:23 IST; 57s ago
 Invocation: 84a63c9a172a416aa213aeda823c7586
       Docs: https://wiki.hyprland.org/Hypr-Ecosystem/hypridle
   Main PID: 2594 (hypridle)
      Tasks: 2 (limit: 17924)
     Memory: 616K (peak: 1.4M)
        CPU: 5ms
     CGroup: /user.slice/user-1000.slice/[email protected]/app.slice/hypridle.service
             └─2594 /nix/store/0bxazkddh9vlf708x3grkxvd8pz1x0li-hypridle-0.1.2/bin/hypridle

Oct 10 10:30:23 Ainz-NIX systemd[2088]: Started Hyprland's idle daemon.

[JohnRTitor]

I'll merge this, no need to hold back a valid fix.