flake.lock: Update

Flake lock file updates:

• Updated input 'nixpkgs':
    'git+https://github.com/NixOS/nixpkgs?ref=nixos-unstable-small&rev=bcc20cad1608fbbe08641e5106c0755cfd0154ad&shallow=1' (2025-08-09)
  → 'git+https://github.com/NixOS/nixpkgs?ref=nixos-unstable-small&rev=d4df8d6cc1ccfd3e4349a1d54e4fb1171e7ec1f5&shallow=1' (2025-08-13)
• Updated input 'treefmt-nix':
    'github:numtide/treefmt-nix/1298185c05a56bff66383a20be0b41a307f52228?narHash=sha256-B%2B3g9%2B76KlGe34Yk9za8AF3RL%2BlnbHXkLiVHLjYVOAc%3D' (2025-08-06)
  → 'github:numtide/treefmt-nix/7d81f6fb2e19bf84f1c65135d1060d829fae2408?narHash=sha256-2vX8QjO5lRsDbNYvN9hVHXLU6oMl%2BV/PsmIiJREG4rE%3D' (2025-08-10)

Author: github-actions[bot]