safecpp: clean up test-to-requirement traceability

Apply the test-to-requirement traceability clean-up described in #522 to the SafeCpp component (`score/language/safecpp/`).

Review every C++ gtest against the current `comp_req__safecpp__...` needs. Add mandated `FullyVerifies` or `PartiallyVerifies` links, `TestType`, `DerivationTechnique`, and self-contained `Description` metadata where a test genuinely verifies a requirement. Reconcile requirement text and test behavior in both directions, and leave non-functional requirements that are verifiable only by inspection without artificial test coverage.

Start by reading the traceability clean-up described in issue #522, then review the C++ gtests under score/language/safecpp/ against the current comp_req__safecpp__... needs. Done means reconciling requirements and test behavior in both directions, adding the specified metadata only where justified, and leaving inspection-only requirements without artificial tests.

Written by the indexing model from the issue text.