build(nix): update dependencies

• Updated input 'fenix':
    'github:nix-community/fenix/80b1a19' (2026-01-09)
  → 'github:nix-community/fenix/334c4b4' (2026-01-10)
• Updated input 'fenix/nixpkgs':
    'github:nixos/nixpkgs/5912c17' (2026-01-07)
  → 'github:nixos/nixpkgs/3497aa5' (2026-01-08)
• Updated input 'fenix/rust-analyzer-src':
    'github:rust-lang/rust-analyzer/ff9a2e8' (2026-01-08)
  → 'github:rust-lang/rust-analyzer/714d047' (2026-01-09)
• Updated input 'nixpkgs-unstable':
    'github:NixOS/nixpkgs/5f02c91' (2026-01-09)
  → 'github:NixOS/nixpkgs/3146c6a' (2026-01-10)

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Author: github-actions[bot]