build(nix): update dependencies

• Updated input 'fenix':
    'github:nix-community/fenix/8067797' (2026-01-18)
  → 'github:nix-community/fenix/d7dc5da' (2026-01-19)
• Updated input 'fenix/rust-analyzer-src':
    'github:rust-lang/rust-analyzer/1cd5183' (2026-01-16)
  → 'github:rust-lang/rust-analyzer/080e703' (2026-01-18)
• Updated input 'nixpkgs-unstable':
    'github:NixOS/nixpkgs/3327b11' (2026-01-17)
  → 'github:NixOS/nixpkgs/bde0902' (2026-01-19)

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Author: github-actions[bot]