Evaluate llvm-cov coverage solution in baselibs

### What

Evaluate the llvm-cov-based coverage generation approach introduced in https://github.com/eclipse-score/communication/pull/549 and referenced from https://github.com/eclipse-score/reference_integration/issues/259.

The goal is to validate how llvm-cov works in the **baselibs** repository (C++ part only) before making the solution reusable in the `score_tooling` module.

### Acceptance Criteria (DoD)

- [ ] llvm-cov is run in baselibs CI (on a branch/test pipeline) and produces a coverage report for C++ code on Linux.
- [ ] The justification mechanism (from communication#549) is validated: at least one justified exclusion is created and correctly represented in the report.
- [ ] A comparison of llvm-cov output vs. existing `bazel coverage` output is documented for at least one representative component.
- [ ] A short findings with actionable recommendations for making the solution reusable in `score_tooling` are added as a comment to this issue.