PR2: Add matlab.unittest suite and MATLAB CI

[iahncajigas]

Summary

Adds deterministic MATLAB test/CI scaffolding for nSTAT:

• run_tests.m local/CI test entrypoint with JUnit output
• tests/ test suite:
  • TestFixtures (fixture presence checks)
  • TestParityAgainstBaseline (legacy + modern parity integration checks)
  • TestPlotStyleApi (plot style API tests; skipped by assumption when PR1 APIs are absent)
• GitHub Actions workflow:
  • .github/workflows/matlab-ci.yml
  • Uses matlab-actions/run-command@v2 on self-hosted macOS runner
  • Uploads JUnit artifact
• Minor housekeeping:
  • .gitignore now ignores test-results/
  • docs/DEVPLAN.md includes run_tests local command

Local verification

Executed on MATLAB 2025b:

addpath('/Users/iahncajigas/Library/CloudStorage/Dropbox/Research/Matlab/nSTAT_currentRelease_Local/tools');
run_tests('IncludeParity',true,'OutputXml',fullfile('test-results','results.xml'));

Observed result:

• TestFixtures: PASS
• TestParityAgainstBaseline:
  • legacy parity PASS
  • modern parity PASS
• TestPlotStyleApi: filtered (expected on branches without PR1 style APIs)
• Overall test run exits success.

Notes

• This PR is intentionally compatible with master both before and after PR1 merge.
• Once PR1 is merged, TestPlotStyleApi executes instead of filtering.