Enable @defer/incremental delivery on the owned-connection path

R429’s owned-connection path releases the pinned connection at operation completion, so a deferred fetcher running after the initial result would use a closed connection. The V0 stance is therefore that incremental delivery stays off: the owned factory never opts in, and GraphitronConnectionInstrumentation.beginExecuteOperation rejects an execution with incremental support enabled outright (pinned by ConnectionLifecycleExecutionTest). Enabling @defer/@stream under owned connections must own the connection-lifetime story: when release happens relative to deferred delivery, how session identity stays mounted (or remounts) for late fetchers, and how that composes with the per-settle re-fire fallback and the tenant-keyed carrier. Named as a follow-on in R429’s @defer section; this item is its tracking home now that the R429 spec is deleted.