[dkasimovskiy]

What & why

Test coverage was generated by JaCoCo but never collected: the coverage jobs in tests.yml were commented out, and nothing blocked PRs that lowered coverage.

This PR collects JaCoCo execution data from all CI test jobs, builds a single aggregate report across all modules, uploads it to Codecov, and configures Codecov statuses to fail when project or patch coverage decreases.

Changes

• .github/workflows/tests.yml
  • unit / box-integration / crud-integration jobs upload their *.exec files as artifacts (matrix jobs get a versioned exec filename so runs do not overwrite each other).
  • new merge-jacoco-report job downloads the exec files into the module target/ dirs and runs ./mvnw -DskipTests verify -pl jacoco-coverage-aggregate-report -am, which builds classes and generates one jacoco.xml, then uploads it to Codecov.
  • removed the dead commented-out merge job.
• jacoco-coverage-aggregate-report/pom.xml
  • added tarantool-spring-data-core and tarantool-spring-data-27…40 dependencies — previously spring-data was missing from the aggregated report entirely.
  • bound report-aggregate to verify; invoking it with -pl without -am produced an empty report because dependencies were not in the reactor.
  • testcontainers is now compile scope in this module (BOM sets test), otherwise its classes are excluded from the report.
• codecov.yml — project and patch statuses use target: auto, threshold: 0%.

Verified locally: aggregate report contains 573 classes, 325 of them from spring-data (including spring-data-core, which is exercised only by the version modules' tests).

Follow-ups (not in code)

• Install the Codecov GitHub App for tarantool/tarantool-java-sdk / add CODECOV_TOKEN secret if required.
• In branch protection for master, require status checks codecov/project and codecov/patch.

Checklist

• Tests — n/a (CI/config change)
• Changelog — n/a
• Documentation — n/a
• Commit messages comply with the guideline

Related issues: —