Make Maven Fmt/ Lint Job Run Faster

From a recent run of the lint job (https://github.com/googleapis/google-cloud-java/actions/runs/15201184035/job/42755490835) took ~30 minutes to run.


Can we make this run faster?

Job details (https://github.com/googleapis/google-cloud-java/blob/80a9d63203bc7e12a8ed2a7cd0eb06450c3ce03e/.github/workflows/ci.yaml#L82) looks to try and run this in parallel.

Additional options to explore:
- Can we only fmt this on modules that have code changes instead of running this for the entire repo?
- Can we only fmt on PRs that have code changes (exclude CI or deps upgrades)?
- Does the fmt plugin to help speed this up natively? Some configurations that we can play around with?

Start with the Maven fmt/lint job in .github/workflows/ci.yaml around line 82 and review the linked run to identify where the roughly 30 minutes is spent. Compare options for limiting work to changed modules or relevant pull requests, and verify that the job remains correct while running faster.

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