nix/flake.lock: Update

Flake lock file updates:

• Updated input 'freetype2':
    'github:wez/freetype2/e4586d960f339cf75e2e0b34aee30a0ed8353c0d?narHash=sha256-%2BFh%2B/k%2BNWL5Ow9sDLtp8Cv/8rLNA1oByQQCIQS/bysY%3D' (2023-06-24)
  → 'github:freetype/freetype/42608f77f20749dd6ddc9e0536788eaad70ea4b5?narHash=sha256-4l90lDtpgm5xlh2m7ifrqNy373DTRTULRkAzicrM93c%3D' (2024-08-12)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/69b9a8c860bdbb977adfa9c5e817ccb717884182?narHash=sha256-5zJyv66q68QZJZsXtmjDBazGnF0id593VSy%2B8eSckoo%3D' (2024-12-31)
  → 'github:NixOS/nixpkgs/d6973081434f88088e5321f83ebafe9a1167c367?narHash=sha256-cuNapx/uQeCgeuhUhdck3JKbgpsml259sjUQnWM7zW8%3D' (2025-01-02)
• Updated input 'rust-overlay':
    'github:oxalica/rust-overlay/04d5f1836721461b256ec452883362c5edc5288e?narHash=sha256-tIl5p3ueaPw7T5T1UXkLc8ISMk6Y8CI/D/rd0msf73I%3D' (2025-01-02)
  → 'github:oxalica/rust-overlay/a599f011db521766cbaf7c2f5874182485554f00?narHash=sha256-6Ta5E4mhSfCP6LdkzkG2%2BBciLOCPeLKuYTJ6lOHW%2BmI%3D' (2025-01-03)