ci: migrate Nix CI to official installer and hestia cache

Swap nix-quick-install-action -> nix-installer-action and
cache-nix-action -> Mic92/hestia/action across every Nix workflow, drop
the now-unneeded cache keys, and run devShell tooling through a
defaults.run.shell. Add gc.yml to trim the hestia cache daily.

.github/workflows/check-generated.yml

@@ -12,6 +12,10 @@ concurrency:
   group: ${{ github.workflow }}-$${{ github.head_ref || github.run_id }}
   cancel-in-progress: true
 
+defaults:
+  run:
+    shell: nix develop --fallback --command bash -e {0}
+
 jobs:
   check-generated:
     runs-on: ubuntu-latest
@@ -29,17 +33,14 @@ jobs:
               - 'go.*'
               - '**/*.go'
               - 'tools/**'
-      - uses: nixbuild/nix-quick-install-action@2c9db80fb984ceb1bcaa77cdda3fdf8cfba92035 # v34
+      - uses: NixOS/nix-installer-action@6b8548fe06acfb0155a50ab5d561accb215764cc # main
         if: steps.changed-files.outputs.files == 'true'
-      - uses: nix-community/cache-nix-action@135667ec418502fa5a3598af6fb9eb733888ce6a # v6.1.3
+      - uses: Mic92/hestia/action@ff07bb902a9968ac0c3d0e51d90a606662a375d8 # main
         if: steps.changed-files.outputs.files == 'true'
-        with:
-          primary-key: nix-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('**/*.nix', '**/flake.lock') }}
-          restore-prefixes-first-match: nix-${{ runner.os }}-${{ runner.arch }}
 
       - name: Run make generate
         if: steps.changed-files.outputs.files == 'true'
-        run: nix develop --fallback --command -- make generate
+        run: make generate
 
       - name: Check for uncommitted changes
         if: steps.changed-files.outputs.files == 'true'