This PR modifies NuttX CI and GitHub Actions, to comply with ASF Policy. Right now, every NuttX Pull Request will trigger 24 Concurrent Jobs (GitHub Runners), executing them in parallel: https://lupyuen.github.io/articles/ci
According to ASF Policy: We should run at most 15 Concurrent Jobs: https://infra.apache.org/github-actions-policy.html
Thus we'll cut down the Concurrent Jobs from 24 down to 15. That's 12 Linux Jobs, 2 macOS, 1 Windows. (Each job takes 30 mins to 2 hours)
(1) Right now our "Linux > Strategy" is a flat list of 20 Linux Jobs, all executed in parallel
(2) We change "Linux > Strategy" to prioritise by Target Architecture, and limit to 12 concurrent jobs
(3) So NuttX CI will initially execute 12 Build Jobs across Arm32, Arm64, RISC-V, Simulator and Xtensa. As they complete, NuttX CI will execute the remaining 8 Build Jobs (for Arm32).
(4) This will extend the Overall Build Duration from [2 hours](https://github.com/apache/nuttx/actions/runs/10817443237) to [2.25 hours](https://github.com/lupyuen4/ci-nuttx/actions/runs/10828246630)
(5) We'll also limit macOS Jobs to 2, Windows Jobs to 1
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