Added a new reusable full-denominator C++ coverage workflow and coverage tooling (target discovery, LCOV processing, denominator validation, local runner script, and unit tests).

[olivembo]

Implemented coverage accuracy fixes:

• Synthetic baseline now applies only to sources missing from runtime LCOV.
• Baseline DA line numbering preserves real source line numbers.
• Branch coverage records are preserved during LCOV merge/filter.
• HTML report generation now resolves source paths with the correct repo root and includes legend output.
• Exclusions parsing now ignores comment lines.

Repo hygiene:

• Python bytecode and cache folders are ignored in git.

[AlexanderLanin]

This belongs somewhere else, as it should be executable locally as well. If all the scripting is here, then its only executable by ci.

[MaximilianSoerenPollak]

I agree with @AlexanderLanin here.
This should be not in CI/CD Repo, but rather in a place that is central for CPP things so it's also enabled to run locally.
Having coverage only be calculatable in CI would be rather bad for workflow and also logically it does not make sense for me.

I haven't checked the details of the implementation, but this IMO does not belong in this Repo. We should keep this truly only for CI/CD related things that do not need to run locally or already have a mechanism to run locally.

[olivembo]

I agree with @AlexanderLanin here. This should be not in CI/CD Repo, but rather in a place that is central for CPP things so it's also enabled to run locally. Having coverage only be calculatable in CI would be rather bad for workflow and also logically it does not make sense for me.

I haven't checked the details of the implementation, but this IMO does not belong in this Repo. We should keep this truly only for CI/CD related things that do not need to run locally or already have a mechanism to run locally.

Would https://github.com/eclipse-score/score_cpp_policies fit?

[MaximilianSoerenPollak]

Would https://github.com/eclipse-score/score_cpp_policies fit?

I can't say for sure as I'm not a codeowner there, but gut feeling tells me it for sure is a much better fit than here.
As it's c++ related & something all of the c++ repos should use anyhow in the end (as far as I know)