perf(ci): switch to nix-quick-install-action for faster CI

Replace cachix/install-nix-action with nixbuild/nix-quick-install-action.
This should reduce Nix installation time from ~30-60s to ~1s on Linux.

Key differences:
- Single-user installation (no daemon)
- Deterministic installation for a given action version
- Minimal overhead optimized for CI environments

Author: ryoppippi

.github/actions/setup-nix/action.yaml

@@ -13,9 +13,7 @@ runs:
   using: 'composite'
   steps:
     - name: Install Nix
-      uses: cachix/install-nix-action@4e002c8ec80594ecd40e759629461e26c8abed15 # v31.9.0
-      with:
-        github_access_token: ${{ github.token }}
+      uses: nixbuild/nix-quick-install-action@c245e13f8a7be373da8a36b4adcce5e0cb7dd3a2 # v30
 
     - name: Install tools from nixpkgs
       shell: bash