[chore] flake.lock: update inputs

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/1c6e20d41d6a9c1d737945962160e8571df55daa' (2024-12-20)
  → 'github:NixOS/nixpkgs/1807c2b91223227ad5599d7067a61665c52d1295' (2024-12-22)
• Updated input 'nixvim':
    'github:nix-community/nixvim/450cccf472f40ae8e3b92eec9e5f4b071693ac85' (2024-12-22)
  → 'github:nix-community/nixvim/8938e09db14d510dcc2f266e8b2e738ee527d386' (2024-12-23)
• Updated input 'treefmt-nix':
    'github:numtide/treefmt-nix/65712f5af67234dad91a5a4baee986a8b62dbf8f' (2024-12-20)
  → 'github:numtide/treefmt-nix/e41e948cf097cbf96ba4dff47a30ea6891af9f33' (2024-12-23)