flake.lock: Update

Flake lock file updates:

• Updated input 'nix-fast-build':
    'github:Mic92/nix-fast-build/8ac62f3' (2026-02-08)
  → 'github:Mic92/nix-fast-build/57f1315' (2026-04-19)
• Updated input 'nix-fast-build/flake-parts':
    'github:hercules-ci/flake-parts/5792860' (2026-02-02)
  → 'github:hercules-ci/flake-parts/3107b77' (2026-04-01)
• Updated input 'nix-fast-build/nixpkgs':
    'github:NixOS/nixpkgs/a48c9db' (2026-01-18)
  → 'github:NixOS/nixpkgs/f731538' (2026-04-18)
• Updated input 'nix-fast-build/treefmt-nix':
    'github:numtide/treefmt-nix/337a4fe' (2026-02-04)
  → 'github:numtide/treefmt-nix/790751f' (2026-04-08)
• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/dd9b079' (2026-02-27)
  → 'github:nixos/nixpkgs/b12141e' (2026-04-18)
• Updated input 'pre-commit-hooks':
    'github:cachix/pre-commit-hooks.nix/6e34e97' (2026-02-25)
  → 'github:cachix/pre-commit-hooks.nix/3cfd774' (2026-04-21)

Author: github-actions[bot]