build(nix): update dependencies

• Updated input 'fenix':
    'github:nix-community/fenix/8456b98' (2025-12-09)
  → 'github:nix-community/fenix/6399553' (2025-12-11)
• Updated input 'fenix/nixpkgs':
    'github:nixos/nixpkgs/f61125a' (2025-12-05)
  → 'github:nixos/nixpkgs/addf7cf' (2025-12-08)
• Updated input 'fenix/rust-analyzer-src':
    'github:rust-lang/rust-analyzer/5e3e9c4' (2025-12-07)
  → 'github:rust-lang/rust-analyzer/fface27' (2025-12-10)
• Updated input 'nixlib':
    'github:nix-community/nixpkgs.lib/e0cad97' (2025-12-07)
  → 'github:nix-community/nixpkgs.lib/2075416' (2025-12-14)
• Updated input 'nixpkgs-unstable':
    'github:NixOS/nixpkgs/677fbe9' (2025-12-09)
  → 'github:NixOS/nixpkgs/23735a8' (2025-12-13)

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Author: github-actions[bot]