feat: update flake.lock (#77)

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/42a1c966be226125b48c384171c44c651c236c22?narHash=sha256-rpqepOZ8Eo1zg%2BKJeWoq1HAOgoMCDloqv5r2EAa9TSA%3D' (2025-04-05)
  → 'github:nixos/nixpkgs/2631b0b7abcea6e640ce31cd78ea58910d31e650?narHash=sha256-LWqduOgLHCFxiTNYi3Uj5Lgz0SR%2BXhw3kr/3Xd0GPTM%3D' (2025-04-12)

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Author: github-actions[bot]