fix: unpack ccache on prefix hit; restore on cpu-runner too

- Unpack: replace cache-hit=='true' gate with a file-existence check.
  actions/cache outputs cache-hit=false on restore-keys prefix hits even
  though the cache IS downloaded, so the old condition skipped unpacking
  and every build ran fully cold despite downloading 1.2GB.
- Restore: match all ephemeral ARC runners by excluding VM name prefix
  (iZ0x) instead of only gpu-runner-*, which missed cpu-runner-* pods.

Author: MrLi000001

.github/workflows/cuda.yml

@@ -54,7 +54,7 @@ jobs:
 
       - name: Restore ccache
         id: ccache
-        if: startsWith(runner.name, 'gpu-runner-')
+        if: ${{ !startsWith(runner.name, 'iZ0x') }}
         uses: actions/cache/restore@v4
         with:
           path: /tmp/ccache.tar.zst
@@ -63,11 +63,12 @@ jobs:
             ccache-cuda-
 
       - name: Unpack ccache
-        if: steps.ccache.outputs.cache-hit == 'true'
         run: |
-          sudo mkdir -p /github/home/.ccache
-          sudo tar -I zstd -xf /tmp/ccache.tar.zst -C /github/home
-          sudo chown -R $(whoami) /github/home/.ccache
+          if [ -f /tmp/ccache.tar.zst ]; then
+            sudo mkdir -p /github/home/.ccache
+            sudo tar -I zstd -xf /tmp/ccache.tar.zst -C /github/home
+            sudo chown -R $(whoami) /github/home/.ccache
+          fi
 
       - name: ccache stats (before build)
         run: |

.github/workflows/test.yml

@@ -68,7 +68,7 @@ jobs:
 
       - name: Restore ccache
         id: ccache
-        if: startsWith(runner.name, 'gpu-runner-')
+        if: ${{ !startsWith(runner.name, 'iZ0x') }}
         uses: actions/cache/restore@v4
         with:
           path: /tmp/ccache.tar.zst
@@ -77,11 +77,12 @@ jobs:
             ccache-gnu-
 
       - name: Unpack ccache
-        if: steps.ccache.outputs.cache-hit == 'true'
         run: |
-          sudo mkdir -p /github/home/.ccache
-          sudo tar -I zstd -xf /tmp/ccache.tar.zst -C /github/home
-          sudo chown -R $(whoami) /github/home/.ccache
+          if [ -f /tmp/ccache.tar.zst ]; then
+            sudo mkdir -p /github/home/.ccache
+            sudo tar -I zstd -xf /tmp/ccache.tar.zst -C /github/home
+            sudo chown -R $(whoami) /github/home/.ccache
+          fi
 
       - name: ccache stats (before build)
         run: |