build(nix): update dependencies

• Updated input 'fenix':
    'github:nix-community/fenix/55106e0' (2026-01-11)
  → 'github:nix-community/fenix/fe00060' (2026-01-12)
• Updated input 'fenix/nixpkgs':
    'github:nixos/nixpkgs/3497aa5' (2026-01-08)
  → 'github:nixos/nixpkgs/ffbc9f8' (2026-01-11)
• Updated input 'fenix/rust-analyzer-src':
    'github:rust-lang/rust-analyzer/e42e8ff' (2026-01-10)
  → 'github:rust-lang/rust-analyzer/dd48777' (2026-01-11)
• Updated input 'nixpkgs-unstable':
    'github:NixOS/nixpkgs/3146c6a' (2026-01-10)
  → 'github:NixOS/nixpkgs/3fbab70' (2026-01-12)

Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]