flake.lock: Update

Flake lock file updates:

• Updated input 'flake-parts':
    'github:hercules-ci/flake-parts/4524271' (2025-09-01)
  → 'github:hercules-ci/flake-parts/80daad0' (2026-01-11)
• Updated input 'flake-parts/nixpkgs-lib':
    'github:nix-community/nixpkgs.lib/a73b9c7' (2025-08-10)
  → 'github:nix-community/nixpkgs.lib/2075416' (2025-12-14)
• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/647e5c1' (2025-09-28)
  → 'github:nixos/nixpkgs/6308c3b' (2026-01-30)
• Updated input 'rust-overlay':
    'github:oxalica/rust-overlay/381776b' (2025-09-30)
  → 'github:oxalica/rust-overlay/a1d32c9' (2026-01-31)

Author: github-actions[bot]