naas-abi-core: key_value versioned-store adapter

[Dr0p42]

Goal

Back the key-value service onto IVersionedStorePort for the auditable / branched code path. The Redis adapter remains as the hot-path option.

Scope

• KeyValue__VersionedStore.py: each key is a uid; each set is a revision.
• theirs / ours merge resolver per key (no semantic merge — values are opaque to the service).
• Pass the existing generic key-value adapter test suite.
• Documentation on when to use which adapter (Redis for hot path, versioned-store for auditable / branched data).

Out of scope

• A coexistence policy enforcing a hybrid Redis-write-through-versioned-store mode (separate issue if demanded).

Acceptance criteria

• Generic tests pass.
• Branching tests pass.
• Performance characteristics documented.

Dependencies

• IVersionedStorePort issue.

References

• Spec: Spec: branching support across naas-abi-core services #865