feat(nix): Implement nix-flake-check hook

[aRustyDev]

Description

Implement a pre-commit hook to validate Nix flakes using nix flake check.

Requirements

• Check for nix command availability with flakes enabled
• Run nix flake check on flake.nix files
• Support both local and remote flakes
• Provide clear error messages for validation failures
• Handle cases where experimental features might not be enabled

Implementation Details

• Location: hooks/nix/nix-flake-check.sh
• Language: bash script
• File pattern: flake.nix

Testing

• Test with valid flake.nix
• Test with invalid flake.nix
• Test with missing inputs
• Test with evaluation errors

Configuration in .pre-commit-hooks.yaml

- id: nix-flake-check
  name: Check Nix flakes
  description: Validates Nix flakes using 'nix flake check'
  entry: hooks/nix/nix-flake-check.sh
  language: script
  files: flake\.nix$