ci: add explicit venv cleanup before setup in all workflows to prevent cache corruption

Added `rm -rf venv` (and `venv-build` where applicable) before venv setup in all CI workflows to ensure clean installations and prevent cache corruption issues. Removed redundant venv corruption detection and rebuild logic from package-tests.yml since explicit cleanup makes it unnecessary.

.gitea/workflows/staking-tests.yml

@@ -35,7 +35,10 @@ jobs:
       - name: Setup Python environment
         run: |
           cd /var/lib/aitbc-workspaces/staking-tests/repo
-          
+
+          # Remove any existing venv to avoid cache corruption issues
+          rm -rf venv
+
           bash scripts/ci/setup-python-venv.sh \
             --repo-dir "$PWD" \
             --venv-dir "$PWD/venv"