build(nix): update dependencies

• Updated input 'fenix':
    'github:nix-community/fenix/8124451' (2026-03-13)
  → 'github:nix-community/fenix/556198c' (2026-03-21)
• Updated input 'fenix/nixpkgs':
    'github:nixos/nixpkgs/fe416aa' (2026-03-12)
  → 'github:nixos/nixpkgs/b40629e' (2026-03-18)
• Updated input 'fenix/rust-analyzer-src':
    'github:rust-lang/rust-analyzer/6254616' (2026-03-12)
  → 'github:rust-lang/rust-analyzer/0cf3e8a' (2026-03-20)
• Updated input 'nixify':
    'github:rvolosatovs/nixify/bcc5e78' (2026-03-13)
  → 'github:rvolosatovs/nixify/3e60834' (2026-03-19)
• Updated input 'nixlib':
    'github:nix-community/nixpkgs.lib/7489b10' (2026-03-08)
  → 'github:nix-community/nixpkgs.lib/a5ed666' (2026-03-15)
• Updated input 'nixpkgs-unstable':
    'github:NixOS/nixpkgs/7569023' (2026-03-11)
  → 'github:NixOS/nixpkgs/9cf7092' (2026-03-18)

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Author: github-actions[bot]