build(nix): update dependencies

• Updated input 'fenix':
    'github:nix-community/fenix/81d6a75' (2026-01-20)
  → 'github:nix-community/fenix/de681af' (2026-02-09)
• Updated input 'fenix/nixpkgs':
    'github:nixos/nixpkgs/e4bae1b' (2026-01-16)
  → 'github:nixos/nixpkgs/d6c7193' (2026-02-08)
• Updated input 'fenix/rust-analyzer-src':
    'github:rust-lang/rust-analyzer/1b8952b' (2026-01-19)
  → 'github:rust-lang/rust-analyzer/c75729d' (2026-02-09)
• Updated input 'nixify':
    'github:rvolosatovs/nixify/66ce96c' (2025-12-19)
  → 'github:rvolosatovs/nixify/18f0d04' (2026-01-30)
• Updated input 'nixlib':
    'github:nix-community/nixpkgs.lib/78975aa' (2026-01-18)
  → 'github:nix-community/nixpkgs.lib/fd92884' (2026-02-08)
• Updated input 'nixpkgs-unstable':
    'github:NixOS/nixpkgs/bde0902' (2026-01-19)
  → 'github:NixOS/nixpkgs/fef9403' (2026-02-08)

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Author: github-actions[bot]