flake.lock: Update (#1928)

Automated changes by the
[update-flake-lock](https://github.com/DeterminateSystems/update-flake-lock)
GitHub Action.

```
Flake lock file updates:

• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/cab52b36dca5a5a368f05bd03fca0b543b5b9a3e?narHash=sha256-Svhx9lHB3wvxDu9UtxilofG3PZqKvfwUzarSIvuGO5g%3D' (2025-12-20)
  → 'github:NixOS/nixpkgs/deefe7fae28c478ef2b0e0f72352233806fc6da2?narHash=sha256-cTpRd20EknSDkfpumLXIlO3UNnx0U3VmC3LUGVj1mRo%3D' (2025-12-27)
• Updated input 'released-nix-unstable':
    'github:nixos/nix/b6dd17d6f2dbed0a5966f40685fd455c4feb6a57?narHash=sha256-YL8nL9rYblWmDlp8StmJYlq58xSPWdwLJDWU0FFbiMI%3D' (2025-12-20)
  → 'github:nixos/nix/8093df5255572bde31f16287feabb155a218004e?narHash=sha256-D3kmmHHrntqLWAR0vu9psv0al0eTN3xcamB7WMKz4oU%3D' (2025-12-27)
• Updated input 'released-nixpkgs-stable':
    'github:NixOS/nixpkgs/c6f52ebd45e5925c188d1a20119978aa4ffd5ef6?narHash=sha256-m5KWt1nOm76ILk/JSCxBM4MfK3rYY7Wq9/TZIIeGnT8%3D' (2025-12-15)
  → 'github:NixOS/nixpkgs/f560ccec6b1116b22e6ed15f4c510997d99d5852?narHash=sha256-BASnpCLodmgiVn0M1MU2Pqyoz0aHwar/0qLkp7CjvSQ%3D' (2025-12-26)
• Updated input 'released-nixpkgs-unstable':
    'github:NixOS/nixpkgs/c6245e83d836d0433170a16eb185cefe0572f8b8?narHash=sha256-G/WVghka6c4bAzMhTwT2vjLccg/awmHkdKSd2JrycLc%3D' (2025-12-18)
  → 'github:NixOS/nixpkgs/3e2499d5539c16d0d173ba53552a4ff8547f4539?narHash=sha256-QEhk0eXgyIqTpJ/ehZKg9IKS7EtlWxF3N7DXy42zPfU%3D' (2025-12-25)
```

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