Oracle/RAS execution-tier coverage for session identity hooks

Session identity mounts through the <sessionState> method hooks (a static <mount> method whose return value is the handle later passed to <unmount>), with execution-tier proof on Postgres only; Oracle stays unit-tier because the build has no Oracle container. The Oracle worked example is the load-bearing one for Sikt’s kernel API (definer-rights package, VPD institution context, RAS CREATE_SESSION/ATTACH_SESSION with the session id as the handle, detach/destroy by handle on unmount), so the mount/unmount contract, handle capture and rebinding, and the outside-any-transaction invariant (autocommit asserted at acquisition, mount running as committed session state) should each be proven against a real Oracle database once a container (or an external test target, like the test.db.url seam the Postgres tiers already use) is available. Originally a follow-on to the shipped connect/disconnect callable form; the method-hook rework keeps the Oracle gap open and this item remains its tracking home.