flake: update inputs (#548)

Flake lock file updates:

• Updated input 'nixpkgs-stable':
    'github:NixOS/nixpkgs/1807c2b91223227ad5599d7067a61665c52d1295?narHash=sha256-Pzyb%2BYNG5u3zP79zoi8HXYMs15Q5dfjDgwCdUI5B0nY%3D' (2024-12-22)
  → 'github:NixOS/nixpkgs/6c90912761c43e22b6fb000025ab96dd31c971ff?narHash=sha256-8T660guvdaOD%2B2/Cj970bWlQwAyZLKrrbkhYOFcY1YE%3D' (2024-12-23)
• Updated input 'rust-overlay':
    'github:oxalica/rust-overlay/fb5fdba697ee9a2391ca9ceea3b853b4e3ce37a5?narHash=sha256-NdhUgB9BkLGW9I%2BQ1GyUUCc3CbDgsg7HLWjG7WZBR5Q%3D' (2024-12-24)
  → 'github:oxalica/rust-overlay/ca249a1d98eff27e92665ac462b9d47f58141925?narHash=sha256-eIUYGDtairggo7%2BJXSwN7b6Zr03BJ7tsZL/U0NkDr0s%3D' (2024-12-25)

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