flake.lock: Update (#21)

Flake lock file updates:

• Updated input 'effekt-nix':
    'github:jiribenes/effekt-nix/4288354' (2026-03-09)
  → 'github:jiribenes/effekt-nix/46c85db' (2026-03-30)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/f8573b9' (2026-03-16)
  → 'github:NixOS/nixpkgs/b63fe7f' (2026-03-28)

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]