hash: clean up test-to-requirement traceability

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

Review every C++ gtest under `score/hash/` against the current `comp_req__hash__...` needs. Add mandated `FullyVerifies` or `PartiallyVerifies` links, `TestType`, `DerivationTechnique`, and self-contained `Description` metadata where the 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 issue #522, then inspect every C++ gtest under score/hash/ alongside the current comp_req__hash__... needs. Reconcile requirement wording with actual test behavior in both directions, adding the specified metadata only where a test genuinely verifies a requirement. Done means the traceability metadata is complete and non-functional requirements verifiable only by inspection have no artificial tests.

Written by the indexing model from the issue text.