Purge self-runner's pip cache weekly (#975)

.github/workflows/cache-purge.yml

+name: Weekly Cache Purge
+
+on:
+  schedule:
+    - cron: '0 0 * * 0' # Every Sunday at 00:00
+  workflow_dispatch:
+
+jobs:
+  purge-cache:
+    runs-on: self-hosted
+
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v3
+
+    - name: Purge pip cache
+      run: |
+        source $HOME/venv/bin/activate
+        echo "$HOME/venv/bin" >> $GITHUB_PATH
+        pip cache purge
+
+    - name: Update dependencies
+      run: |
+        pip install --upgrade pip
+        pip install -e "python[all]"
+        pip install flashinfer -i https://flashinfer.ai/whl/cu121/torch2.4/ --force-reinstall

.github/workflows/e2e-test.yml

@@ -31,7 +31,6 @@ jobs:
         source $HOME/venv/bin/activate
         echo "$HOME/venv/bin" >> $GITHUB_PATH
 
-        pip cache purge
         pip install --upgrade pip
         pip install -e "python[all]"
         pip install flashinfer -i https://flashinfer.ai/whl/cu121/torch2.4/ --force-reinstall

.github/workflows/unit-test.yml

@@ -31,7 +31,6 @@ jobs:
         source $HOME/venv/bin/activate
         echo "$HOME/venv/bin" >> $GITHUB_PATH
 
-        pip cache purge
         pip install --upgrade pip
         pip install -e "python[all]"
         pip install flashinfer -i https://flashinfer.ai/whl/cu121/torch2.4/ --force-reinstall