Add env var that forces the vendored caching module when set to
'true', decoupling module selection from the Develocity access key.
Set it centrally in init-integ-test so all tests use the vendored
module by default.
Add a dedicated legacy caching integration test that overrides the
env var to 'false' to verify the legacy module works correctly.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Daz DeBoer