Update Nix flake inputs

[github-actions]

Automated changes by the update-flake-lock GitHub Action.

Flake lock file updates:

• Updated input 'fenix':
    'https://api.flakehub.com/f/pinned/nix-community/fenix/0.1.2439%2Brev-3107255abfe4f2d1c3eee7a3e2f5a5eb6f2200fe/019a3e7f-523d-7e82-b791-0e92cf55a0a9/source.tar.gz' (2025-11-01)
  → 'https://api.flakehub.com/f/pinned/nix-community/fenix/0.1.2471%2Brev-df3c2e78ec13418f85c1f26e77a50f865ec57d38/019ad905-65fc-7ba6-8d92-a0b2cf1c6ea6/source.tar.gz' (2025-12-01)
• Updated input 'fenix/rust-analyzer-src':
    'github:rust-lang/rust-analyzer/2e2e3eb' (2025-10-31)
  → 'github:rust-lang/rust-analyzer/d646b23' (2025-11-30)
• Updated input 'nixpkgs':
    'https://api.flakehub.com/f/pinned/DeterminateSystems/secure/0.888552.266/019a79d1-4378-7098-86c6-65eafc8d3dc6/source.tar.gz' (2025-11-12)
  → 'https://api.flakehub.com/f/pinned/DeterminateSystems/secure/0.904649.313/019b4714-003c-7b50-a3aa-ffc368440845/source.tar.gz' (2025-12-22)

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