GH-1188: Reduce test workflow waste

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Summary

This PR reduces wasted GitHub Actions time in the Test workflow by removing redundant rebuilds, improving caching, and skipping integration work when it is not relevant.

What changed

• Removed clean from ci/scripts/test.sh so the test phase reuses the classes compiled earlier in the job instead of deleting and recompiling them.
• Narrowed the Maven/Docker cache key to POM changes, so source-only edits do not invalidate the dependency cache.
• Enabled Maven dependency caching on the macOS and Windows test jobs.
• Restricted the workflow push trigger to main and tags.
• Added pull-requests: read so the integration job can inspect changed files.
• Added a WIP guard for the integration job.
• Made the integration job run only when integration-relevant files changed.

Partially addresses #GH-1188

Note: The changes on this PR were highlighted and addressed with AI assistance