[Elizabeth Craig (ecraig12345)]

Summary

Reduce e2e test setup and process-startup overhead to make the suite less susceptible to intermittent timeouts on slower machines, particularly Windows CI runners. Production task-runner behavior and test timeouts are unchanged.

Changes

• Move the remote-fallback cache-policy matrix into direct provider tests that assert provider calls, retaining a small CLI smoke test.
• Add prepare() to link fixture workspaces and the built Lage package using directory junctions instead of running yarn install. Reuse the shared fixture linker and default these fixtures to npmClient: 'npm'.
• Add runLage() to launch the built CLI directly with Node, reusing arguments from the fixture's root package.json scripts.
• Keep real Yarn installation and script execution for the basic Yarn and repository-path-with-spaces e2e tests. Make fixture installation asynchronous and name it yarnInstall() to distinguish it from lightweight preparation.
• Add focused Monorepo unit tests for preparation, argument handling, and validation, with subprocess execution and Git operations mocked.