[FSSDK-13238] ci: retry only failed unit tests and upload results on failure

[muzahidul-opti]

Summary

Unit tests now retry only the failing tests, and test results are uploaded when a job fails.

 unittests job
-  for attempt in 1 2 3:            # rebuild + re-run all 620 tests each time
-    run_unit_tests.sh || rm -rf build COVERAGE
+  run_unit_tests.sh                # xcodebuild -retry-tests-on-failure -test-iterations 3
+                                   # → only failed tests re-run, no rebuild
 Archive Test Results
-  if: steps.unit_tests.outcome != 'success'   # implicit success() && … → never ran
-  path: build/Logs                            # never existed
+  if: failure() && steps.unit_tests.outcome == 'failure'
+  path: COVERAGE/Logs/Test                    # single .xcresult with every retry
-timeout-minutes: 90
+timeout-minutes: 45

Why: the iPad job on the #660 merge commit (run 37558972075) failed after 3 full-suite attempts, each turning up different flaky tests. The archive step was skipped, so no results were available to debug them.

Evidence

• Before: iPad job, 3 × 620 tests, a new set of flakes each attempt → ❌, and Check on failures (Archive Test Results) was skipped
• After (local, temporary test that fails only on its first run):

  Retrying tests on failure. Running tests repeatedly up to 3 times.
  testTempFlaky (Iteration 1 of 3) failed
  testTempFlaky (Iteration 2 of 3) passed   ← only the failed test re-ran
  ** TEST SUCCEEDED **  exit=0
  

• CI on this PR: all 4 unit test jobs

Merge Danger

Door: two-way (CI-only, revert restores the loop)
Blast Radius: unit test jobs only. Infra failures (e.g. simulator boot) are no longer auto-retried; use "Re-run failed jobs". Flaky tests are still masked, but the .xcresult now records them.

Issues

• FSSDK-13238

🤖 Generated with Claude Code

[coveralls]

coverage: 93.929%. remained the same — muzahid/native-test-retry into master